Erm, do you really want to be with a girl who is saying that kind of stuff behind your back? She is obviously enjoying all of the male attention, but to say that she would like to have sex with them behind your back...?? I personally think that is taking things a little too far. There are issues of trust etc. and you obviously are not sure - hence why you looked at her msn chat and her text messages. I know how you feel as I've been there myself. Not sure about you, but after finding something similar out from my ex-boyfriend, I never felt I could trust him, so had to walk away from the relationship. If I were you, I'd think about giving her an ultimatum - you or him. What she is doing to you right now is really no better what her ex-boyfriend did to her. The question you have to ask yourself is do you trust her enough and will you get over this. If the answer is no, then you have to walk away...