So this is going to sound shallow/stupid but...?

I'm going to try and make this as short as I can. My boyfriend and I have been together 4 years, we live together. Lately, he's been treating me really bad, but I'm attached, so I'm letting him get away with it. Plus, its good 80% bad 20% and all relationship have some bad. My sisters getting married on Saturday and he's been a jerk every step of the way. Anything I have to do with her, he refuses to join, and then makes my life hell for going. (don't touch on how stupid is I'm putting up with it, I already know) so here's my question. We get along like I said 80% of the time, but when its bad its REALLY bad. Screaming at me, calling me names, mocking my family, making threats...just bad. When we get along its fantastic, as perfect as I could ever wish for. We also live together so we benefit from eachother. We have our belongings basicaly combined so if we break up and he moves out, I lose the tv in my bedroom, blu ray player, ps3, and lots of other stuff. I'm not super materialistic, which is why all those things belong to my bf and not me. I don't spend my money on things like that, but he always does. That being said, if we break up, he's taking all his stuff with him obviously, and I've gotten used to it. It makes things really ruff. We've tried splitting before. I always just miss the hell out of him ( i tend to forget the bad and focus on the good) and on top of that I miss the comfort he offered. I feel safe at my appartment when he's there, we cuddle in bed, we watch all the same shows, we do meals together, he helps me when things are to heavy ( i live on the third floor) basically, my life is just a million times easier with him around and I miss him to death when he's gone. I just don't know what to do anymore. I feel stuck. If he goes, my comfort, and possesions go with it. It makes it really hard to cope, and I don't know what to do. He's just gotten so horribly nasty. He's refusing to go the wedding itself by the way, no matter how many times we talk about it, and I went to my sis's bacheloreette party weekend 2 weeks ago, and he argued with me for 3 days before i left, refused to talk to me while i was gone, and partied and got drunk friday and sat. night with friends (and a girl i despise and asked him to stay away from because although she has a boyfriend, she's a total skank) oh and bought cigarettes after not smoking for over a year and then had a HUGE blowout when I got home (which included him lighting a cigarette in our home, which neither of us allow, we have a balcony). Does anyone have advice for how to get out of this cycle or how to cope if he does move out? He also refuses to leave like 2 weeks ago and says I can pack all his stuff, then breaks down and says he's sorry, so it's really hard. Please give me some advice. I'm so lost. Sorry this turned out long...