Sheesh, not even once did somebody suggest "Keep sex for marriage"? That's the interesting thing - the standard in this thread seems to be "sex is meant for a relationship, else somebody will get hurt". However, then there's the fight over whether he/she was in a relationship. Now, if they kept sex for marriage, then this wouldn't have been a problem at all - most people are fairly certain whether they are married or not!
I might be old-school, but I'm guessing there would be a whole lot less hurt if this rule was followed. And yes, you could try and get to the point of saying "see sex as just sex", but the fact is, it WILL be an emotional and intimate thing for most people, ALWAYS.
@Problemo - sorry buddy, my comments are not really helping your case. Sorry you got hurt!
We also didnt mention slavery or burning witches at the stake.
It might have solved the issue, it also might have caused one of them to cheat purely for sex. It also might have meant that should they get married, they might not have been sexually compatible or sexually satisfied with their partner and result in divorce