Infidelity and jealousy

Defining it

Infidelity is a breach of an agreement, which means it is defined by the agreement rather than by the act. Couples differ substantially in where the line sits: emotional closeness with someone else, flirting, messaging, pornography, paid services, or physical contact. A significant proportion of conflict arises from a line that was assumed rather than stated.

Consensual non-monogamy is not infidelity, because the agreement includes it. Concealed non-monogamy within an agreed-monogamous relationship is.

Prevalence

Reliable measurement is difficult because it depends on self-reported behaviour people are motivated to conceal, and on definitions that vary between studies.

The US General Social Survey, which asks about sex with someone other than a spouse while married, has consistently found lifetime rates of roughly 20 percent for men and 13 percent for women. The gender gap has narrowed over successive cohorts, and among adults under 30 recent GSS analyses find rates that are comparable or slightly higher for women.

Rates rise with relationship length and with opportunity, and vary substantially by measurement method — anonymous computer-administered surveys yield higher reported rates than face-to-face interviews.

Why it happens

Research on stated reasons (Selterman et al., 2019, surveying 495 people about their motivations) found the most common were: anger or retaliation, lack of love, low commitment, need for variety, feeling neglected, situation and opportunity, self-esteem seeking, and sexual desire. Reasons frequently combined, and the reason predicted the outcome — infidelity motivated by anger or lack of love was more likely to end the relationship than infidelity motivated by situation or variety.

The finding that recurs across this literature: infidelity is more often about the person who does it than about the partner's inadequacy. This matters, because the assumption that a betrayed partner failed in some way is both common and usually wrong.

Jealousy

Jealousy is a normal emotion, not a character defect and not proof of love. It signals a perceived threat to something valued and typically points at a specific unmet need — reassurance, time, priority, or information.

Useful jealousy is treated as information: identify the underlying need and ask for it directly. Destructive jealousy becomes surveillance — checking phones, tracking location, restricting contacts, demanding constant accounting — which is controlling behaviour, is associated with intimate partner violence, and does not reduce jealousy. It reliably erodes the trust it is trying to protect.

Evolutionary psychology's claim of a sex difference in jealousy type — men more distressed by sexual infidelity, women by emotional infidelity — comes largely from forced-choice hypothetical questions. Studies using continuous measures and real experiences find much smaller and less consistent differences, and cross-cultural replication is mixed. Treat the claim as contested rather than established.

Impact

Discovery of infidelity produces symptoms resembling acute stress reaction: intrusive thoughts, sleep disruption, hypervigilance, appetite change and rumination. A subset meet criteria for PTSD-like presentations. This is a genuine psychological injury, and dismissing it as overreaction is unhelpful and inaccurate.

Recovery

Relationships do recover, and a substantial minority end. Couples therapy outcome research finds that couples who disclose infidelity during therapy do about as well over time as couples presenting with other difficulties, though the initial distress is higher — a finding from Marín, Christensen and Atkins (2014) following couples for five years.

What the evidence associates with recovery:

• Full disclosure by the involved partner, rather than information emerging in stages. Staggered discovery is repeatedly identified as the most damaging pattern.
• Ending the outside relationship completely and verifiably.
• Genuine remorse focused on the impact, not on the discovery or on the involved partner's own distress.
• Transparency for a period, offered rather than demanded.
• Patience with non-linear recovery. Setbacks are the normal shape of it; anniversaries and reminders trigger recurrence of acute distress for a long time.
• Understanding why it happened, which is what prevents recurrence.
• Professional support. Emotionally focused therapy and integrative behavioural couple therapy both have evidence for infidelity recovery specifically.

What does not work: demanding the betrayed partner move on quickly, using the infidelity as a permanent argument-winner, minimising, comparing, or attempting to relitigate the details repeatedly. Forgiveness is not owed, and ending the relationship is a legitimate outcome rather than a failure of the recovery process.

Prevention

The recurring finding is that explicit agreements outperform assumed ones. Discuss what counts as a breach, revisit it as circumstances change, address dissatisfaction while it is small, and treat attraction to other people as normal and not itself a betrayal. Concealment is the variable most consistently associated with harm — in this literature and in the research on pornography and on non-monogamy alike.

Sources

• Selterman D, Garcia JR, Tsapelas I. "Motivations for extradyadic infidelity revisited." Journal of Sex Research, 2019.
• Labrecque LT, Whisman MA. "Attitudes toward and prevalence of extramarital sex and descriptions of extramarital partners in the 21st century." Journal of Family Psychology, 2017.
• Marín RA, Christensen A, Atkins DC. "Infidelity and behavioral couple therapy: relationship outcomes over 5 years following therapy." Couple and Family Psychology, 2014.
• Gordon KC, Baucom DH, Snyder DK. "An integrative intervention for promoting recovery from extramarital affairs." Journal of Marital and Family Therapy, 2004.
• Harris CR. "A review of sex differences in sexual jealousy, including self-report data, psychophysiological responses, interpersonal violence, and morbid jealousy." Personality and Social Psychology Review, 2003.
• Roos LG et al. and reviews on post-infidelity stress and trauma symptoms.

Last reviewed: August 2026.