Few topics in modern dating generate as much confusion, disagreement, and raw emotion as the question of what counts as cheating. In an era of shifting norms around sexuality, gender, and relationship structure, the boundaries that were once assumed are increasingly being questioned — and not always for straightforward reasons. One particular conversation that comes up repeatedly: whether a woman kissing another woman while in a heterosexual relationship constitutes infidelity. Here’s an honest, psychology-informed look at the arguments made on both sides — and what the evidence actually says about attraction, boundaries, and relationship agreements.
The Core Issue: What Is Cheating, Actually?
Psychology and relationship research are fairly consistent on one point: cheating is defined not by the specific act, but by whether the act violates the understood or explicitly agreed boundaries of the relationship. Infidelity, at its core, is a breach of trust — an action that one or both partners believe constitutes betrayal of the relational agreement.
This means that what constitutes cheating varies between relationships — not because people get to make up whatever rules suit them in the moment, but because couples genuinely differ in what they agree their relationship involves. With that framework in mind, let’s look at the arguments often made.
1. Fluid Sexuality Is Recognised by Psychology as Real
Lisa Diamond’s influential research on sexual fluidity documents what many women experience: that attraction isn’t always fixed, binary, or tied to a stable “orientation” in the way earlier models assumed. For some women in heterosexual relationships, attraction to another woman exists alongside their attraction to their partner — not as contradiction, but as part of a more complex sexuality.
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This psychological reality doesn’t determine whether kissing another woman is cheating — but it does complicate simplistic framings. A woman who identifies as bisexual or has fluid sexuality may experience her attraction to women as qualitatively different from her attraction to men — not as a threatening competition for her partner, but as a different dimension of who she is.
2. Some Couples Have Explicit or Implicit Agreements That Apply Here
Some relationships operate with explicit or implicit permissions around specific contexts — a kiss at a party, same-sex contact in particular settings, behaviours agreed not to constitute infidelity because the relationship between the partners is specific and agreed. These agreements exist, and within them, an act that would be cheating in another relationship is simply not cheating in this one, because it falls within the agreement.
The key word is agreement. An implicit assumption on one person’s part that “this is fine” doesn’t constitute a relational agreement. A genuine mutual understanding — ideally explicit — is what makes a difference here.
3. Many Heterosexual Men Don’t Experience Same-Sex Female Contact as a Threat
Psychologically, one of the dimensions of infidelity pain is the threat it poses — to security, to sexual self-concept, to the primary bond. Research on jealousy and infidelity finds that different types of infidelity activate different levels of jealousy in different people. Many heterosexual men report that same-sex contact between their female partner and another woman activates significantly less jealousy than equivalent male-female contact — a finding that reflects both cultural norms and genuine differences in perceived threat.
This doesn’t mean it’s not cheating if it violates the relational agreement. But it contextualises why some couples, in practice, treat same-sex contact differently from opposite-sex contact.
4. The Emotional Versus Physical Distinction Matters
Research consistently shows that emotional infidelity — forming a deep romantic attachment outside the relationship — causes at least as much harm to relationships as physical contact, and sometimes more. A brief, purely physical kiss can be experienced as qualitatively different from sustained emotional intimacy with another person — a distinction that many couples make in practice when assessing the significance of boundary-crossing behaviour.
Whether a specific act of same-sex kissing is primarily physical or has an emotional attachment dimension is highly relevant to how it’s likely to affect the relationship — and how the partners themselves will experience it.
5. Context and Consent Shape the Meaning
An act done openly, with the partner’s knowledge, or in a context where both parties understand what happened and how it relates to their relationship is psychologically very different from an act that is hidden, lied about, or managed in a way that involves deception. The deception, in infidelity research, is often identified as one of the most damaging elements — not just the act itself, but the loss of trust that comes from discovering you were misled.
A kiss that happens and is openly acknowledged, discussed, and processed between partners — particularly if it falls within an area where boundaries were genuinely unclear — is fundamentally different from one that is actively hidden.
6. The Relationship Agreement Is What Ultimately Determines This
All of the above arguments are interesting and worth understanding — but they ultimately point toward the same answer that psychology consistently arrives at: what defines infidelity is the relational agreement, not the act in the abstract. If the couple has not explicitly or implicitly agreed that same-sex contact falls outside the definition of cheating in their relationship, and one partner kisses another woman without discussion, the act is likely to be experienced as a betrayal — regardless of any psychological arguments about fluidity, threat levels, or context.
The conversation about relationship agreements — what we’re agreeing to, what falls inside and outside that agreement, how we handle ambiguity — is one of the most important conversations couples can have. It’s more useful than trying to find external psychological validation for whether a specific act “counts” as cheating. For more on what honest, open communication in relationships looks like, these signs of a truly healthy relationship offer a useful baseline.
What If You Discover This Has Happened?
If you’re reading this because something has happened in your relationship, the first step is an honest conversation — not a debate about definitions, but a genuine exchange about how both of you experienced what happened, what it means for the relationship, and what you need from each other going forward. The question “does this count as cheating?” is less useful than “how did this affect us, and what do we need to do now?”
Couples therapy is a valuable resource for navigating precisely these conversations — particularly when both partners are trying to be honest but struggling to hear each other’s experience without defensiveness. Navigating independence and boundaries in relationships is an ongoing process, not a single conversation.
Frequently Asked Questions
Is it cheating if my girlfriend kissed a girl at a party?
The honest answer depends entirely on the agreements in your relationship. If you’ve never discussed whether same-sex contact falls inside or outside your relational agreement, there’s genuine ambiguity — and the conversation you need to have is about what your relationship actually means to each of you, not about whether the act technically qualifies. If you feel hurt, that feeling is real and valid regardless of how the act is categorised.
Does psychology say it’s not cheating?
No. Psychology doesn’t have a universal ruling on what constitutes cheating, because the definition is relational rather than universal. What psychology does say is that infidelity is defined by agreement violation and perceived betrayal — and that the impact of infidelity is shaped by context, meaning, and the specific nature of the relationship affected. The psychological frameworks inform the conversation without replacing the couple’s own agreement as the definitive standard.
Can our relationship recover from this?
Many relationships navigate similar situations and emerge with greater clarity about their agreements and a stronger foundation for honest communication. What determines recovery is usually not the act itself but the quality of the conversation that follows — whether both partners feel heard, whether the person who hurt the other is genuinely accountable, and whether both parties want to invest in working through what happened rather than using it as a justification for a predetermined conclusion.
Further Reading & Sources
- Dr. Lisa Diamond, University of Utah – research on sexual fluidity
- Buss et al.: sex differences in jealousy (evolution & psychology)
- Psychology Today: the psychology of infidelity
Cassandra Simpson is a wellbeing and relationship writer with a BSc in Psychology and five years of experience working in community mental health support. She writes about love, friendship, boundaries, and the emotional work of belonging — drawing on both academic grounding and the hard-won perspective that comes from navigating her own relationship patterns, friendships, and personal growth in real time. Cassandra trained as a peer support facilitator and has spent years exploring attachment theory, interpersonal dynamics, and the psychology of connection. Her writing is shaped by a deep belief that most relationship struggles come not from failure, but from the absence of honest, accessible information about how human connection actually works.
