Infidelity definition

In this post, we will define infidelity including the origins of the word, and how becoming unfaithful evolves including the five acts of infidelity.

It often involves a careless drift of your attention, when cruising the internet.

define infidelity

Infidelity meaning

The word infidelity comes from the Middle English “infidelite.” This, in turn, was borrowed from Middle French infidelité, which  borrowed from Latin infidēlitāt-, infidēlitās “faithlessness, inconstancy,” from infidēlis “unfaithful, disloyal.”

So we have been defining infidelity for well over a thousand years…because it is an incredibly common human experience.


Research tells us that infidelity begins with a subtle pattern of conflict avoidance. Avoiding conflict increases emotional distance. Each day our behaviors either keep us closer and connected or promote drift and distance with our partner. Infidelity is the end result.

The five acts of infidelity

1. Comparing your partner to others.

Gottman talks about “comparison theory” as essential to all forms of infidelity. We do this when comparing our romantic partner to any sort of attractive “other” whether a stranger, a close friend, or pixelated porn.

define infedelity

Fidelity involves more than a romantic or sexual relationship. It’s a stance of trust and transparency.

Infidelity involves actively turning away from your partner and toward someone or something else in secret. There are many kinds of betrayal but the essence of all betrayal is secrecy.

2. Breaking previously agreed upon boundaries

Lovers develop agreed-upon relational boundaries. Clarity matters more than the rules or boundaries you create. Clear boundaries maintain lasting romantic bonds.

Betrayal is a subtle, almost glacially slow shift away from agreed-upon boundaries and toward parallel lives.

3. Broken Trust 

Cross-cultural studies have revealed the fundamental fact that trust is the most important factor in healthy marriages.

When we cannot trust our partner to be there for us, we slide into secret-keeping. The further apart we grow, the more open our hearts become to forming new attachments and romantic relationships outside of marriage.


Intimate trust keeps us vulnerable and open, able to love deeply and profoundly. When trust erodes, it is gradually replaced by secrecy and betrayal. It can also be a lazy series of compromises.

  • Why bother to engage in conflict with your remote intimate partner? 
  • Why try to talk about your growing loneliness and sense of isolation?
  • Why open up when marital conflict could result?

However, conflict maintains intimate bonds. It is challenging to talk about the difficult issues: the hassles, hurts, and frustrations.

4. Secret-keeping

Disengagement spares yourself short-term discomfort and assures long-term emotional disconnection. Unfaithful men are less driven by their unhappiness with their wives than most unfaithful women.  As a consequence, they are often more bewildered by having an affair. Infidelity happens one secret at a time.

5. The careless drift of attention

Infidelity is also a careless drift of attention. You feel entitled to gawk at attractive others, or flirt openly. You may begin to cover your tracks. This is hard to do in an age of social media, transcripts, or Facebook pages.

Social media is redefining infidelity. A bored few hours cause our attention to drift and we impulsively engage in flirtatious talk. Within seconds we are crossing boundaries.


As couples therapists, we define infidelity not only as having a sexual or emotional affair with someone else but as a broader set of behaviors that begin with emotional withdrawal and secret-keeping. This intensifies loneliness. We stop sharing our deepest thoughts and feelings. From there, the act of infidelity can include five elements including comparing your partner to others, breaking boundaries and trust, keeping secrets, and carelessly allowing your attention to drift to betrayal.


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Daniel Dashnaw

Daniel is a Marriage and Family Therapist and the blog editor. He currently works with couples online and in person. He uses EFT, Gottman Method, Solution-focused and Developmental Models in his approaches. Daniel specializes in working with neurodiverse couples, couples that are recovering from an affair, and couples struggling with conflict avoidant and passive aggressive behavior patterns.

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