i think... he's getting pushed around and doesn't know how to get out of it. i knew this girl in college who was SUCH A BITCH but her boyfriend was adorable and did everything she asked him to. i kinda felt bad and wondered why he was with her. but who knows, maybe she's soft around him, lets down her guard. if it works for them, then who am i to judge... but from the outside, it doesn't seem fair to him.
He should just talk to her, and if she still doesn't change then it would be best if he leaves before he gets hurt. I would say she doesn't deserve him, but I'm not aware of the whole situation, so I have no right to say anything like that.