One of my best friends has a boyfriend who is a complete a**hole. He once cheated on my friend and when got caught "fixed" things with my pal, but now he was caught red handed doing the same thing again. The thing is, my friend is easily fooled and while he's very mad at him right now, we feel that this insecure jerk of a bf will get his way by wooing him. He did not even dare to explain things, nor say a genuine sorry, he avoids talking about it even, and he talks to my friend in a cutesy way like "I miss my bunny, I wanna hug him" to pacify my friend, as if what he did is as simple as spilling juice on his shirt. How can we (me and our other friends) make our friend realize that this should be the last straw and that it is quite obvious that he deserves someone better than this phony clown who have some serious psychological issues?
As much as you want to help your friend, it has to be his choice to leave the relationship. It sounds like he's having a heart Vs mind battle within himself at the moment, so just be there for him to vent with. By the sound of it, the relationship will probably end at some point and you'll need to be there to help him through the breakup as well. Peace! (*hug*)
I concur with mangotree. While the temptation is strong to jump in and "save" him from this unhealthy relationship, it really isn't your place. What you might be able to do is talk to your friend about what he wants in a relationship and ask if he's really getting what he needs in this one... but not lead him specifically. He'll feel much better about it if he comes up with the answers himself. I think it's also probably reasonable to be honest with him about what you've seen and how you've seen his boyfriend shuck and jive... but leave it at that. If your friend doesn't see it or disagrees, then it's his choice. This sort of stuff is really hard, but you have to let him go through his own process. You can encourage him to really think about what he wants, but the rest is really up to him.
It's hard, my friend is in the same position. I would say that being the friend telling them their boyfriend is horrible only makes them resent you. The only guy is the person they think they "love". Being anything other then supportive can often lead to you being pushed out, you end up the baddy. It will fall apart on its own, just make sure you are there to help pick up the pieces. I'm sorry I can't be more helpful, but patience will let them sort it out.