If you truly care about her, you need to tell her ASAP. Three months given to a cheating douchebag sucks, but the longer you stay silent, the worse for her.

Original Poster. :)

Wow I feel for you

Tell her. She is probably going to be pissed off at you (unfortunately the female mind works bizarre ways in these cases) but if she knows what and who is good for her, she will dumps that sleaze and still be your friend. If she does not, at least you have done what is right. It would be much much worse if you didn’t tell her and she found out anyway. Besides, who knows what that idiot might tell her? He is obviously untrustworthy and could blame it on you.

Open poophole ..ok no

You slept with your friends boyfriend and you think YOU have an FML? I think your friend should be on here.

I hope you told her.

He's the douchebag because you had a one night stand with him? I think he's a douche for having sex with you while in a relationship with your friend. However, I don't think you get to call names when you were a willing participant in the sex. I feel this is your friends FML, after all it was your choice to let him put his dick in you. You hold responsibility for that fully!

Silly rabbit tricks are for kids.

Tell her. She needs to know ASAP, especially if she considers it a serious relationship. She can't get mad at you because you didn't know it was her boyfriend when you slept with him.