4 Reasons Why Infidelity Occurs—Even In Happy Relationships

It's valid to assume that a happy, loving partner would never cheat. However, according to psychological research, this sadly is not the case.

By Mark Travers, Ph.D. | March 03, 2025

It's one of the most perplexing betrayals—when someone in a seemingly happy relationship strays. Conventional wisdom suggests that people cheat because something is missing: passion has faded, communication has broken down or resentment has taken root. But the truth is, many affairs happen not out of dissatisfaction, but for far more complex psychological reasons.

Some people cheat despite loving their partner. They may deeply value their relationship and still find themselves drawn to infidelity. This contradiction can be confusing for both the betrayed partner and even the person who cheated themselves. But why does this happen? What hidden forces drive someone to risk something they cherish?

Here are four deeper psychological factors behind why some people cheat—even in happy relationships.

1. The Allure Of Novelty And The Dopamine Chase

Romantic love is deeply tied to the brain's dopaminergic reward system, the same neural network that drives motivation, pleasure and reinforcement. In the early stages of a relationship, this system is highly active, flooding the brain with dopamine—the neurotransmitter responsible for the intoxicating rush of attraction. Every glance, touch and late-night conversation feels electric, reinforcing the desire to pursue and focus on a specific partner.

But over time, this initial high fades. Research using fMRI scans has shown that romantic love transitions from a dopamine-fueled motivation system to a more stable, attachment-driven state supported by oxytocin and vasopressin—hormones that deepen trust and bonding. While this shift is natural and necessary for lasting commitment, some people struggle with the loss of early-stage excitement.

For those who crave constant stimulation, an affair can feel like a quick way to reintroduce that intoxicating new love feeling. This doesn't mean they want to leave their relationship—many people who cheat still feel deeply connected to their partner. But the temptation of an exhilarating, risk-fueled experience can override their better judgment.

Here's what you can do—instead of seeking novelty outside the relationship, you can actively reignite your own dopamine-driven excitement. The same reward pathways that create initial attraction can be stimulated through shared new experiences, such as surprising each other, traveling spontaneously, exploring new hobbies together or deepening intimacy in fresh ways. Romantic love doesn't have to lose its intensity over time—it simply requires intentional effort to keep the brain engaged and excited within the relationship.

2. Fear Of Deep Vulnerability

Paradoxically, some people cheat not because they feel disconnected, but because they feel too connected. For individuals with avoidant attachment tendencies, deep emotional intimacy can feel overwhelming, triggering fears of losing autonomy, becoming too dependent or exposing vulnerabilities they've long protected.

Those who grew up in environments where love was conditional, inconsistent or even harmful may have learned that closeness leads to pain. As a result, true intimacy—where they are fully seen and emotionally invested—can feel unsettling.

Cheating, then, becomes an unconscious way to create distance, allowing them to regain a sense of emotional control. The affair isn't necessarily about the other person—it's about buffering themselves from the vulnerability of deep commitment. A new, less-intense connection can feel "safer" than the emotional exposure required in a long-term bond.

A 2013 study published in Social Psychological and Personality Science offers insight into how to navigate this fear and bridge the attachment gap. The study highlights two key findings:

• Building trust over time reduces attachment avoidance, making commitment feel safer for those who struggle with intimacy.
• Supporting a partner's personal growth and independence lowers attachment anxiety, helping emotional closeness feel less restrictive.

True security in relationships doesn't come from avoiding dependence but from recognizing that love and personal autonomy can coexist.

3. The Identity Crisis—'Am I Still Me?'

Long-term relationships bring two lives together—routines intertwine, identities shift and priorities blend. While this can foster deep connection, it can also lead to an identity crisis, especially for those who strongly associate self-worth with independence, spontaneity or adventure.

Over time, some may feel they've lost touch with the version of themselves they used to be—the person who was single, carefree or exploratory. They might begin to see themselves more as a partner than as an individual, leading to a sense of stagnation.

Research on the self-expansion model suggests that people have a fundamental motivation to broaden their sense of self—either by deepening relationships or by pursuing new, stimulating and challenging experiences. When this innate drive for self-expansion is unfulfilled within the current relationship, individuals may seek it elsewhere—including through infidelity.

Cheating, in this case, isn't necessarily about rejecting a relationship but about reclaiming a lost sense of self. The affair becomes a misguided attempt at self-exploration, a way to recapture freedom, desirability or excitement that seems absent in daily life. However, research suggests that self-expansion doesn't require stepping outside the relationship—it can thrive within it.

Rather than seeking individuality through infidelity, cultivate personal growth inside the relationship. Engage in hobbies that are just for you, maintain friendships outside the partnership and carve out solo experiences that reinforce your independence. The key to a fulfilling relationship isn't sacrificing autonomy—it's ensuring that love and personal growth coexist, rather than compete.

4. Unconscious Self-Sabotage

Some people cheat not because they are unhappy, but because they don't believe they deserve happiness. When someone has grown up in chaotic or emotionally unstable environments, a healthy, secure relationship can feel foreign, even unsettling. Instead of embracing stability, they subconsciously anticipate its end and take preemptive action to disrupt it.

A 2010 study on attachment development and emotional abuse suggests that individuals who experience rejection, control or hostility in childhood often develop insecure attachment styles, which impair emotional regulation, create negative self-perceptions and interfere with the ability to sustain intimacy. If love was unpredictable in early life, they may internalize the belief that happiness is temporary, love always comes with betrayal, or stability is too good to last.

As a result, when they find themselves in a fulfilling relationship, they may feel disoriented or anxious, waiting for something to go wrong. Infidelity, in this case, becomes an unconscious defense mechanism—a way to reaffirm their internal belief that relationships always end in pain. By sabotaging their own happiness, they regain a sense of control over an outcome they already fear.

Breaking this cycle requires self-awareness and healing from past attachment wounds. If you find yourself pushing people away when things are going well, ask yourself:

• "Do I struggle to trust happiness in relationships?"
• "Do I assume things will fall apart even when there's no evidence?"
• "Am I repeating patterns from past relationships or childhood?"

Understanding the why behind infidelity doesn't excuse it, but it does offer a path to healing. If a betrayal has already occurred, the most important question isn't just "Why did this happen?" But "How do we grow from here?"

Are you secure in your relationship, or do you crave excitement, viewing other partners as the best way to find it? Take the Relationship Satisfaction Scale to find out.

A similar version of this article can also be found on Forbes.com, here.