Why Do People Cheat? What the Research Actually Says
The Biggest Myth About Infidelity
One of the most common beliefs about infidelity is that people only cheat because they're unhappy in their relationship.
It's an understandable conclusion. If someone has an affair, it seems logical to assume something must have been deeply wrong at home. In some cases, that's true. Chronic conflict, emotional disconnection, unresolved resentment, loneliness, or unmet relational needs can increase the likelihood of infidelity.
However, the research tells a much more complicated story.
Studies consistently show that relationship dissatisfaction is a risk factor for infidelity—but it is not the risk factor. Many people who have affairs describe their primary relationship as unhappy, while others report being reasonably satisfied or even happy before the affair began. In other words, a struggling relationship may make infidelity more likely, but it does not fully explain why people cheat.
Two individuals can experience the same dissatisfaction and respond in entirely different ways. One seeks couples therapy. Another initiates difficult conversations. A third decides to end the relationship before pursuing someone else. Yet another begins an affair. The relationship may create vulnerability, but it doesn't determine the response.
This highlights an important principle in relationship science: there is no single pathway to infidelity.
People often ask, "Why did they cheat?" as though there is one motive. In reality, infidelity is better understood as a broad category of behavior than a single psychological phenomenon.
Two people can both have affairs despite getting to that point through entirely different psychological processes.
One person's affair may emerge from years of emotional disconnection within their relationship. Others may develop after weak boundaries with a coworker gradually become emotional intimacy. Someone else may be seeking novelty, external validation, excitement, revenge, or escape from emotional distress. For another person, infidelity may reflect longstanding attachment insecurities, impulsivity, entitlement, or deeply held beliefs about commitment.
The behavior may look similar from the outside, but the psychological processes underneath can be remarkably different.
This is why researchers have identified numerous factors that can contribute to infidelity beyond relationship satisfaction. These include poor boundaries, opportunity, novelty seeking, attachment insecurity, difficulty regulating emotions, impulsivity, self-deception, a desire for external validation, entitlement, and personal values surrounding commitment. These factors rarely operate in isolation. Someone who feels emotionally disconnected from their partner may also have weak boundaries with a coworker, be struggling with low self-esteem, and encounter increased opportunity during a stressful period of life.
Rather than searching for one explanation, researchers have increasingly come to understand infidelity as the product of multiple interacting influences.
This also helps explain why experts sometimes appear to disagree about why people cheat. An evolutionary psychologist may emphasize mating strategies and opportunity. An attachment researcher may focus on insecurity or fear of intimacy. A couples therapist may examine emotional disconnection and relationship dynamics. A neuroscientist may explore reward processing, impulsivity, and self-control.
These perspectives are not necessarily competing explanations. More often, they are describing different pieces of the same puzzle.
Understanding this complexity is important because it changes the questions we ask. Instead of looking for a single cause, researchers increasingly ask what combination of individual characteristics, relationship dynamics, situational factors, and personal choices made a particular affair possible.
The researchers in the following sections each illuminate one part of that larger picture. Together, their work provides a more complete understanding of why people cheat than any single theory can offer.
What Different Researchers Have Found
No single researcher has fully explained why people cheat. Instead, each has examined the question through a different scientific lens. Some have focused on relationship dynamics, others on attachment, personality, sexuality, evolutionary pressures, or emotional needs. Together, their work paints a much richer picture of infidelity than any one theory alone.
Shirley Glass: Affairs Often Begin with Boundaries, Not Intentions
Psychologist Shirley Glass, often referred to as one of the pioneers of modern infidelity research, challenged the popular image of affairs as impulsive sexual encounters between strangers. Her clinical work suggested that many affairs begin much more gradually.
Glass argued that emotional affairs often develop when healthy boundaries begin to erode. A friendship with a coworker becomes increasingly personal. Private conversations replace conversations with one's partner. Emotional intimacy gradually takes place outside the primary relationship. Rather than one singular decision, infidelity may emerge through a series of small boundary crossings that gradually normalize increasing intimacy.
One of Glass's most influential observations was that people often protect the new relationship while becoming more guarded with their primary partner. Personal struggles are shared with the affair partner but withheld from the spouse. Emotional energy gradually leaves the primary relationship and goes toward the affair partner.
From Glass's perspective, preventing infidelity is often less about resisting temptation in a single moment and more about maintaining clear emotional and physical boundaries.
John Gottman: Betrayal Often Begins Before the Affair
Relationship researcher John Gottman views infidelity as one possible outcome of relationship deterioration rather than an isolated event.
Drawing from decades of research on couples, Gottman emphasizes emotional disengagement, unresolved conflict, resentment, loneliness, and missed opportunities for connection. Partners continuously make "bids" for attention, affection, and emotional responsiveness. When those bids are repeatedly ignored or rejected, emotional distance can grow.
Importantly, Gottman does not argue that relationship problems cause affairs. Many unhappy couples remain faithful, and many satisfied couples experience infidelity. Instead, he suggests that emotional disconnection can create conditions that make an affair more likely if other vulnerabilities are also present.
His work also discusses repair. Couples who recover from infidelity are often those who become willing to examine not only the affair itself but also the broader patterns that existed before it while still holding the unfaithful partner accountable for the decision to betray the relationship.
Esther Perel: Affairs Can Reflect a Search for the Self
Psychotherapist Esther Perel has offered one of the most widely discussed perspectives on infidelity by shifting attention away from what people are leaving in the primary relationship and toward what they may be seeking by engaging in an affair.
According to Perel, affairs are not always driven by dissatisfaction with one's partner. Sometimes they reflect a longing for a different version of oneself.
People may seek novelty, vitality, freedom, aliveness, adventure, curiosity, or a temporary escape from the routines and responsibilities that accumulate over years of adult life. The affair may become less about the third person and more about rediscovering aspects of one's own identity that feel lost.
Perel also emphasizes that long-term relationships require balancing two competing human needs: security and excitement. While stable relationships provide safety and predictability, people also possess a desire for novelty, mystery, and exploration. For some individuals, these competing needs become difficult to reconcile.
Her perspective does not excuse infidelity but broadens the conversation beyond simple explanations such as unhappiness or sexual dissatisfaction.
David Buss: Evolution Shapes Sexual Behavior
Evolutionary psychologist David Buss approaches infidelity from an entirely different perspective.
His research suggests that human mating behavior has been shaped, in part, by evolutionary factors. Across human history, reproductive challenges differed for men and women, potentially leading to somewhat different patterns of jealousy, mate preferences, and responses to infidelity.
Buss's work has found that, on average, men tend to report greater distress over sexual infidelity, whereas women tend to report greater distress over emotional infidelity. Although these differences are averages, not universal rules, his research proposes that they may reflect different reproductive concerns that evolved over time.
More broadly, Buss argues that opportunity, attraction to alternative partners, desire for sexual variety, and mating strategies may all contribute to understanding why infidelity occurs.
While evolutionary psychology has generated considerable debate, it provides one piece of the broader puzzle by highlighting biological influences alongside psychological and relational ones.
Justin Lehmiller: Motivations Are Remarkably Diverse
Sex researcher Justin Lehmiller has demonstrated that there is no single motivation for infidelity.
His work suggests that people report a wide variety of reasons for cheating, including anger, emotional neglect, loneliness, low commitment, sexual dissatisfaction, novelty seeking, curiosity, low self-esteem, revenge, situational opportunity, and feeling desired or validated.
Importantly, these motivations frequently overlap. Someone may simultaneously feel emotionally disconnected from their partner, struggle with poor boundaries, and experience increased opportunity. Human motivation is rarely explained by one variable alone.
Lehmiller's research reinforces an important principle: asking, "Why do people cheat?" may be the wrong question. A more accurate question is, "Which combination of factors contributed to this particular person's decision?"
How These Perspectives Fit Together
At first glance, these researchers can seem to disagree with one another.
Shirley Glass emphasizes boundaries. John Gottman highlights relationship dynamics. Esther Perel focuses on identity and desire. David Buss examines evolutionary influences. Justin Lehmiller documents a wide range of motivations.
So which one is right?
In many cases, they all are.
Infidelity is not a single psychological phenomenon. It is a behavior that can emerge from many different combinations of biological, psychological, relational, and situational influences. Each researcher is examining one piece of a much larger system.
For some people, the process begins with an individual vulnerability. They may struggle with impulsivity, poor emotional regulation, insecure attachment, or a strong need for external validation. These characteristics do not cause infidelity on their own, but they can increase susceptibility under certain circumstances.
For others, the primary relationship itself creates vulnerability. Emotional distance, chronic conflict, resentment, loneliness, or a lack of intimacy may leave important needs unmet. Again, these experiences do not make betrayal inevitable or acceptable. Many couples navigate these challenges without either partner becoming unfaithful. But they may create conditions in which an affair becomes more tempting.
Then there are situational factors. Opportunity is a factor. Spending significant time with an attractive coworker without boundaries, traveling frequently without one's partner, maintaining weak boundaries in close friendships, experiencing major life transitions, or using alcohol can all make crossing relational boundaries more likely.
Finally, there is the decision itself.
Regardless of the vulnerabilities that exist, infidelity ultimately involves a series of choices. Someone decides to continue texting. They agree to meet privately. They justify crossing boundaries. They continue despite recognizing the potential consequences.
Psychology helps explain why those choices become easier for some people than for others, but it does not eliminate responsibility for making them.
Another important insight from this research is that affairs rarely begin the moment two people become physically involved. More often, they develop gradually. Boundaries are crossed. Rationalizations are made. Emotional investment grows. Secrets accumulate. What eventually looks like a single act of betrayal is often the endpoint of a much longer psychological process.
This is why prevention is about recognizing the small decisions that come before it: maintaining healthy boundaries, addressing relationship problems directly, communicating unmet needs, managing stress effectively, and being honest with yourself when attraction to someone else begins to grow.
Taken together, these perspectives suggest that asking, "What caused the affair?" may be too simplistic.
A more accurate question is:
What combination of individual characteristics, relationship dynamics, situational factors, and personal choices made this affair possible?
That question reflects what decades of research consistently show: infidelity is almost never explained by one variable alone. It is usually the product of multiple interacting influences, with personal responsibility remaining central.
Understanding those interacting influences does not excuse betrayal. It helps us understand how seemingly ordinary people sometimes make extraordinary violations of trust—and, perhaps more importantly, how those violations can be prevented before they ever occur.
What This Means for Couples
If there is one practical lesson to take away from decades of infidelity research, it is this: preventing betrayal is about much more than simply loving your partner.
Most people enter relationships believing they would never cheat. Yet many individuals who have affairs once held that same belief. Infidelity often develops gradually, through ordinary human vulnerabilities interacting with specific circumstances, rather than through a sudden abandonment of one's values.
That reality has important implications for couples.
Don't assume you're immune.
One of the strongest protections against infidelity is recognizing that no one is completely immune to temptation. Believing, "That could never happen to me," can actually make people less attentive to the subtle boundary crossings that often precede affairs.
Humility creates vigilance. It encourages people to take boundaries seriously before they become necessary.
Protect your boundaries before you need them.
Shirley Glass's work reminds us that most affairs begin in everyday conversations.
Couples benefit from discussing what constitutes appropriate boundaries with coworkers, friends, former partners, and social media connections. Waiting until attraction has already developed is much more difficult than establishing expectations early.
Healthy boundaries are less about restricting one another and more about protecting the relationship both partners have chosen to build together.
Address problems instead of assuming they'll resolve themselves.
Research consistently suggests that unresolved conflict, emotional disconnection, loneliness, and resentment can increase vulnerability to infidelity. While these experiences do not cause affairs, they are notable and deserve attention.
Couples who regularly discuss disappointments, unmet needs, changing expectations, and emotional distance are often better positioned to repair small fractures before they become larger ones.
Stay curious about each other.
Long-term relationships naturally become more predictable over time. The challenge is preventing predictability from becoming emotional disengagement.
Continue asking questions. Learn who your partner is becoming, not just who they were when you met. Share new experiences together. Maintain affection, appreciation, and playfulness. Continue pursuing one another rather than assuming the relationship will maintain itself.
Research consistently shows that intimacy is not a static achievement—it is an ongoing process of remaining emotionally engaged with another person.
Take responsibility for your own vulnerabilities.
Not every risk for infidelity exists within the relationship.
Some people struggle with external validation, poor impulse control, conflict avoidance, novelty seeking, or difficulty maintaining boundaries. Others find themselves particularly vulnerable during periods of stress, grief, burnout, or major life transitions.
Understanding your own patterns is one of the most important forms of prevention. Self-awareness allows people to recognize situations where they may be more likely to rationalize behavior that conflicts with their values.
Recognize that trust is built.
Trust is often thought of as something that is lost after an affair. In reality, it is built—or challenged—through thousands of everyday interactions.
Keeping promises. Being honest about uncomfortable feelings. Respecting agreed-upon boundaries. Turning toward one another during moments of stress. Repairing conflicts instead of avoiding them.
These small behaviors form the foundation that helps relationships withstand future challenges.
Remember that healthy relationships require both partners.
Perhaps the most important implication of this research is that couples should distinguish between understanding the relationship and assigning responsibility for infidelity.
Relationships are co-created. Both partners influence communication, intimacy, conflict, and emotional connection. Those dynamics deserve honest examination because they affect the health of the relationship. Infidelity, however, is an individual decision.
A couple may share responsibility for improving their relationship, but only the person who chose to violate the relationship bears responsibility for that choice. Recognizing this distinction allows couples to examine their relationship honestly without shifting blame onto the betrayed partner.
Ultimately, the goal is not to create a relationship where cheating is impossible. No relationship can eliminate every temptation or guarantee every future choice.
The goal is to build a relationship—and individual habits—that make honesty easier than secrecy, communication easier than avoidance, and commitment stronger than momentary gratification. While no couple can control every circumstance they will face, they can create the conditions that make trust far more likely to endure.
The Better Question to Ask
Why did they cheat?
It's an understandable question. When trust has been broken, our minds search for a single explanation that will make the experience feel predictable. If we can identify the reason, perhaps we can make sense of what happened—or protect ourselves from it happening again.
The problem is that this question assumes there is one answer.
Decades of research suggest otherwise.
Infidelity is not explained by a single cause, personality trait, or relationship problem. It emerges from a complex interaction of individual vulnerabilities, relationship dynamics, situational factors, opportunity, personal values, and, ultimately, personal choices.
That is why asking, "Why did they cheat?" is often less useful than asking more specific questions.
What vulnerabilities were present?
What needs, beliefs, or motivations were influencing their decisions?
What boundaries were crossed before the affair began?
What relationship dynamics created vulnerability, and what individual factors made betrayal seem like an acceptable solution?
These questions acknowledge that human behavior is rarely as simple as we wish it were.
For individuals who have been betrayed, understanding these pathways can sometimes reduce the tendency to search for a single flaw in themselves. Affairs are not always a referendum on a partner's worth, attractiveness, or adequacy. While relationship difficulties can contribute to vulnerability, they never remove responsibility from the person who chose to violate the relationship.
For those who have been unfaithful, the research offers a different opportunity. Rather than settling for explanations like "I was unhappy" or "It just happened," it encourages a deeper examination of the psychological processes that led to those decisions. Lasting change rarely comes from shame. It comes from understanding the patterns, vulnerabilities, and rationalizations that made the behavior possible in the first place.
And for couples hoping to protect their relationship, perhaps the most valuable lesson is this: healthy relationships are strengthened by intentionally building trust, communicating openly, maintaining healthy boundaries, and taking responsibility for both the relationship and oneself.
In the end, the research points toward the fact that people do not cheat because of one thing.
They cheat because a unique combination of factors converges at a particular moment—and because, somewhere along that path, they choose to cross a boundary.
While examining these influences does not erase the trauma of betrayal, it remains essential to acknowledge that personal responsibility is the core of every choice. By familiarizing yourself with the science, however, you can begin to identify meaningful strategies to strengthen the foundation of your partnership and proactively mitigate the vulnerabilities that can lead to infidelity.