This is a really interesting question. I talked about it with a group of people one time and found an interesting gender distinction. The women (me included) thought it would be easier to forgive sexual infidelity (a one night stand for example) if it didn't really "mean anything" meaning no emotions were involved. But we would have a harder time forgiving an ongoing emotional affair (in which our partner truly falls in love with someone else but without having sex).

The men on the other hand said they didn't mind an emotional affair but if their partner cheated, they would immediately break up.

I wonder why this is. For me, sex can be completely separated from love. I have had sex with people I didn't care about (not that this is the ideal situation of course). And if I had a partner who had sex with someone one time and then never thought of them again, I wouldn't find it that big a deal. But true infidelity of emotions would hurt me much more.

I was just wondering why there is such a strict gender divide there.