Some people will say snogging someone else is totally fine if you're in a relationship. And for those in open relationships, sleeping with someone else can be totally legit.
But with the ever-changing face of technology, the lines surrounding fidelity become even more blurred.
Some of us have sent a sext or photo of ourselves in a *cough* compromising position. But kind of shockingly, one third of Brits now claim that sending an explicit or sexually suggestive message to someone other than your partner is totally acceptable.
Apparently, we don't think that counts as cheating these days.
In the past year alone, 8 per cent admitted to exchanging flirty or erotic messages with someone that wasn't their partner.
Most agreed that sending a naked pic was naughtier than the odd flirty message. And a majority of them, in a survey conducted by lawyers Slater and Gordon, said the exchange of such messages let to suggestions of actually having sex.
Rup Rai, who works for the firm, told The Metro: "'With more people having access to social media and advances in technology, we have seen a rise in the number of clients coming to us who think their partner has crossed the line and committed adultery, but not in the traditional sense.
"What some might consider a harmless bit of fun – like sending flirty messages or explicit pictures, others consider to be detrimental to their relationship and cause as much hurt and upset as physically cheating."
For exclusive competitions and amazing prizes visit Reveal's Facebook page NOW!