Best friend's Bf

So my best friend of five years also roommate has a bf in which she's been dating for 2years. ever since I could rember he's just left a bad taste in my mouth. I know my best friend isn't happy with him 90% of the time but I feel like she doesn't want to be alone. Now he doesn't beat her or abuse her or anything. But in my in my eyes he's selfish and could care less about how she feels about things. It's either his way or no way. He's also the type of guy into fashion so you know for sure he's WAY too into himself and cares what other people think about him and he likes to be seen ALL the time. Besides all that I think him also growing up being the only child plays a major role as to why he acts the way he does. But at the end of the day I'm always there for my best friend but I'm a bit over her complaining about him every other day breaking up getting back together if she's going to continue to put up with him. I think she deserves way better because she's the complete opposite of him she's the type that will give you her last dime. I don't want to enterfere because it's ultimately her decision on whether she's going to be with him or not. So has anyone been in this situation if so how did you deal with it.