Some people are adamant that a text counts as cheating, while others, like Ross from Friends, think anything goes because you were on a break.
The issue arises when two people in a relationship have… different ideas about what constitutes cheating.
Luckily, we can now settle the debate with some cold, hard research.
According to a recent survey of 3,342 Ashley Madison members, emotional cheating feels just as deceitful as physical, as 55% of the respondents believed that forming a deep emotional bond with someone else counted as one of the worst forms of cheating.
The sending of erotic photos and texts were shortly behind, with approximately 44-46% of the respondents believing these counted as cheating.
Surprisingly, about a third of the respondents believed that maintaining an online dating profile is just as bad as spending actual time with an ex partner.
While only 13% believed that fantasising about someone else was cheating, the act of thinking about someone else during sex was considered cheating by 18% of the respondents.
According to sex and relationship therapist Dr Tammy Nelson, people decide to cheat.
“People make a conscious choice to cheat, it’s not typically something that people fall into,” says Dr Nelson.
“Despite defining what infidelity means to one another, one or both people in a relationship could still make the choice to seek an extra-marital affair when their needs aren’t being met," she added.
She explained that a conversation about needs and desires is important.
"An alternative conversation to have is one that outlines what it is that each partner needs from the other to feel happy and satisfied in the relationship, and how to talk about it when they don’t feel that," says Dr Nelson.
So we still aren't quite sure whether the cave man was cheating... unless, of course, he was having an emotional affair with the woman in the cave next door.