If you knew that a friend's significant other was cheating on him or her, would you tell your friend the truth or keep it to yourself? View other answers

I would confront the S.O. before anything else (not the least because some people are in open relationships). Then I would talk to someone I trust, to make sure that I'm not being utterly stupid. But if I did that and still knew, I would tell my friend - it's what I'd want.

(See, that's the thing with lies - it's much easier to think lying is okay if you don't put yourself in the shoes of the lied-to. I know - I read it in a book!)

(But seriously - it's true, and it's a good book: Lying: Moral Choice in Public and Private Life by Sissela Bok. I recommend it.)