so i have been seeing this guy for awhile now and recently we have some what drifted apart. well about two weeks ago we hooked up, which is nothing out of the ordinary. well i found out today that he has had a girl friend for about a month now. so that makes me the other girl. and puts me in a weird situation because that girl that he is dating is our friends sister. so i feel like i should tell him that his sister got cheated on but i feel like if i do that he will just tell me im lying or wont believe me, but if i dont say anything and later on it comes out he be mad at me for not saying anything....
what do i do?

I'm a big advocate for staying out of situations like this...nothing good will come out of it for you. He'll probably hang himself anyway.

I'd probably have a go at him for putting you in the situation and tell him what an absolute piece of work he was (in slightly less nice terms, of course).

Cheers
Di

It's none of your friends business what is happening in his sister's romantic life. Don't say anything to anyone and steer clear of this guy you hooked up with, obviously.

I would actually probably do the opposite as advised because I would be royally pissed at people keeping secrets like this. To me, this guy shouldn't have the expectation that the girls he cheats with will be silent. It wouldn't matter if she didn't believe me, clearing my conscience and trying to do right by her is more important than her opinion of me. I think that your friend is inconsequential in this equation...he's not involved in this, it's you, the boy, and the girlfriend.

I'd do it in a basic letter or e-mail. Simple, concise note saying "I'm an ex of his, I thought he was still single and we got together. I just learned that he is in a relationship with you. I hate feeling like I'm keeping a secret, and I wanted to let you know. I want you to know that I will be avoiding him in the future, and that I won't tell anyone else. I understand that your relationship is between you and him and that I will respect that privacy."

I accept that most people will not agree with my stance, however, I think that knowing about a moral or ethical transgression and not doing anything is immoral as well. Cheating on a test or cheating on a person...I won't say that keeping the secret is "just as bad" as doing the transgression, but it's still pretty bad.

Thanks for the advice. I ended up confronting him about the situation because I was driving me nuts. We actually talked a lot of things through an it turns out I got some what false info. Which makes me feel relieved because he wasn't actually with this girl at that time. But needless to say I'm re-evaluating my choice in friends at the moment.