My roommate, also a very good friend of mine, is with his girl basically 24/7. We used to hang out and go chill. I can't remember the last time I went to catch a movie with him. He is always going to chickflicks with her. I end up just renting the DVD of the movies (action, horror) myself.
Regardless of how I feel, I can't say squat because, as many of you have mentioned, I am not the one he is banging so I have no say in the matter.
I also feel that he is going out of his way to accommodate her. In the beginning when they started dating, she did the "let's be friends" thing on him and he became devastated. Who was there for him then? Me! Then she comes crawling back and he takes her up on it without making her sweat (even though he had discussions with me on how he planned to make her "work" for it).
A few months ago, he told me that she was b!tching at him non-stop and that he was going to put his foot down. Needless to say that never happened. What changed? He just threw out his man card and seccumbed to whatever she demanded.
This is all from a guy, who, when single, touted the "bros before hos" motto around.
The point is, there's nothing you can do about it. When this girl stakes him through the heart, the only thing you can do is be there for him. That's what it means to be someone's friend.