Why Do People Cheat? The Psychology of Infidelity

Few relationship events are as painful — or as widely misunderstood — as infidelity. Popular culture offers simple stories: cheaters are bad people, or cheating means the relationship was already over. Research tells a more complicated story. Psychologists study infidelity as a behavior with predictable correlates: who is more likely to stray, under what conditions, and what follows. None of that excuses it — but understanding it beats myth.

This article is educational. It explains what research finds about infidelity: what counts as cheating, how common it is, what is associated with it, and what happens afterward. It is not moral judgment, not therapy, and not a verdict on your relationship. Our article on trust in relationships covers how trust breaks and whether it can be repaired; this one covers the phenomenon itself.

What Counts as Infidelity

Researchers typically define infidelity as secret romantic or sexual involvement with someone other than one’s partner — the secrecy being as central as the act. But the boundaries are genuinely contested, and the research reflects that. Studies distinguish sexual infidelity (physical involvement) from emotional infidelity (romantic emotional involvement without sex), and people disagree sharply about which hurts more and which “counts.” Online behavior — secret messaging, dating profiles, intimate chats — has blurred the lines further.

This matters for reading any statistic: prevalence estimates depend entirely on definitions. A review of the literature notes that infidelity extends well beyond marriage, with people in dating and cohabiting relationships reporting higher rates than married people (Fincham & May, 2017). Reviews commonly cite figures around 20–25% of marriages experiencing infidelity at some point — but the honest footnote is that definitions, samples, and timeframes vary so much that any single number should be read as approximate, not exact.

What Research Associates With Infidelity

No single cause explains cheating. Research points to a convergence of factors, each shifting the odds:

• Relationship dissatisfaction. Lower satisfaction and lower commitment are among the most consistent correlates. This is intuitive — but it is worth noting the direction isn’t fully settled: dissatisfaction may lead to infidelity, or the guilt and secrecy of infidelity may erode satisfaction. Most likely both operate.
• Opportunity and context. Infidelity requires opportunity, and opportunity is situational: travel, workplaces, social circles, and now dating apps all expand it. This is one reason rates are higher in dating than in marriage — younger relationships combine more opportunity with less investment binding them.
• Individual differences. Research on predictors of extradyadic sex has examined demographic, interpersonal, and personality factors (Mark, Janssen, & Milhausen, 2011). Traits like a more unrestricted sociosexual orientation — comfort with sex outside committed relationships — are associated with higher likelihood.
• Attachment patterns. Avoidantly attached people — those uncomfortable with closeness — show greater interest in romantic alternatives, which is associated with infidelity (DeWall et al., 2011). The mechanism is understandable: when intimacy itself feels threatening, alternatives feel safer.
• Perceived alternatives. Consistent with the investment model covered in our relationships overview, perceiving attractive alternatives is associated with lower commitment — and lower commitment with infidelity.

Two cautions. First, these are correlates, not profiles: most dissatisfied or avoidant people do not cheat, and some satisfied people do. Second, the popular story that “cheating means the relationship was already dead” is often wrong — many people who cheat report loving their partner. Infidelity is frequently about opportunity, compartmentalization, or unmet needs alongside genuine attachment, not instead of it.

The Aftermath: What Follows Discovery

The research on aftermath is sobering. A major review summarizes that infidelity is reliably associated with poorer mental health — particularly depression and anxiety — in those affected, and with relationship dissolution (Fincham & May, 2017). Across 160 societies, infidelity has been identified as the single most commonly cited cause of marital dissolution.

For the betrayed partner, the experience often includes obsessive review of the past (“what did I miss?”), damage to self-confidence, and difficulty trusting — not only the partner but one’s own judgment. For the partner who cheated, common responses include shame, defensiveness, or compartmentalization. For the relationship, three broad paths emerge: ending, continuing with the wound unaddressed, or the slow work of rebuilding — the last of which our trust article examines honestly, including that repair is sometimes possible, slow, and never guaranteed. Whether to forgive is a separate question from whether to rebuild, and it has its own evidence base — see forgiveness in relationships.

Can Infidelity Be Predicted or Prevented?

Honestly: imperfectly. The correlates above shift probabilities; they don’t identify future cheaters. And “prevention” advice that amounts to surveillance — monitoring a partner’s phone, restricting their friendships — doesn’t prevent infidelity so much as poison the relationship it claims to protect. Our article on relationship red flags draws this line clearly: vigilance is not intimacy.

What the research does support is less dramatic: relationships with higher satisfaction, stronger commitment, and fewer perceived alternatives have lower rates. Those aren’t tricks; they’re the ordinary maintenance the rest of this site’s cluster describes — responsiveness, repair after conflict, and attention to the relationship as a living thing. There is no hack that infidelity-proofs a partnership. There is only the unglamorous work of keeping it good.

Key Takeaways

• Infidelity is typically defined as secret romantic or sexual involvement with someone other than one’s partner; sexual and emotional infidelity are studied separately, and online behavior has blurred the boundaries.
• Reviews commonly cite ~20–25% of marriages affected, with higher rates in dating relationships — but definitions vary, so read any number as approximate (Fincham & May, 2017).
• Correlates include relationship dissatisfaction, opportunity, unrestricted sociosexuality, avoidant attachment, and perceived alternatives — these shift odds; they don’t profile individuals.
• Infidelity is reliably associated with poorer mental health and is among the most commonly cited causes of marital dissolution across cultures (Fincham & May, 2017).
• Surveillance doesn’t prevent cheating; satisfaction, commitment, and ordinary relationship maintenance are what the evidence actually supports.

References

1. Fincham, F. D., & May, R. W. (2017). Infidelity in romantic relationships. Current Opinion in Psychology, 13, 70–74. https://doi.org/10.1016/j.copsyc.2016.03.008
2. Mark, K. P., Janssen, E., & Milhausen, R. R. (2011). Infidelity in heterosexual couples: Demographic, interpersonal, and personality-related predictors of extradyadic sex. Archives of Sexual Behavior, 40(5), 971–982. https://doi.org/10.1007/s10508-011-9771-z
3. DeWall, C. N., Lambert, N. M., Slotter, E. B., Pond, R. S., Jr., Deckman, T., Finkel, E. J., Luchies, L. B., & Fincham, F. D. (2011). So far away from one’s partner, yet so close to romantic alternatives: Avoidant attachment, interest in alternatives, and infidelity. Journal of Personality and Social Psychology, 101(6), 1302–1316. https://doi.org/10.1037/a0025497

Keep Exploring

• Trust in Relationships — how trust breaks and whether it can be repaired.
• The Psychology of Breakups — when relationships end: why it hurts and what helps.
• The Psychology of Relationships — the pillar overview.