What will you do? if you found out your bf still keep contact with his ex gf.  He said both of them are friend but my friend found out they have sex sometimes.One of my friend found that for a while but she keep quiet doing as nothing happen but it's disturb her mind.  Her bf still treat her good when he's with her.  She don't want to make the fire in the relationship.   Should she keep quiet like this? or do something? I don't know what should I suggest her.  maybe some people should share oppinion here. 

he's lying and being unfaithful. Tell your friend to drop him like a hot coal. : )

"my friend found out they have sex sometimes" ?????? ----- huh? How could she find out?

and there are so many 'levels' of friendship depends on how we define it.

Dr_Sassy brings up a good point, how did she find out about them having sex? However, if he did have sex with another woman, she should get rid of him ASAP. How good he treated her, shouldn't even come into consideration given the fact that he cheated on her. If he does it once, he'll do it again.

why is it important how she found out??

break up as soon as possible! otherwise she will always have a feeling of not being able to trust him, and trust is one of the most important things in a relation

Frans65, The only reason that it's important is to make sure that it's just not gossip and that it's true. For instance if she found out from someone who found out from someone else, the truth could be something totally different. Getting all the facts first, always makes for a more informed decision. And do agree with you that trust is one of the most important things in a relationship.

Mark, indeed she needs to be sure first! but i asume she checked her information at least 3 times, it would be terrible if someone is gossiping about this and break up a couples relation

Yes, she check til sure not just about gossip. I really feel sorry with that. seem she so confuse to keep it or say it out. now it's like she worry all the time when she have to go out and didn't stay home for sometime. all she need it is stay with him all the time that's not eazy to be like that. I feel sad when I saw she cried.

Er yah. if hes cheating dump him. just make sure thats its not hearsay...

or talk to the other girl.

he try to be nice to her as he knows that he have done something bad ...cheating on her....just stay away from him....

dont try to talk and get back with eachother .... love is something about trust...if one break it ... we will never get it back...

Tell her to go out and get laid.

cut his **** off..not so hard....

tell your friend this wisdom:

always believe the bf if you know whats good for you