What should I do now that my boyfriend has started to be violent toward me?

We have always had a lot of problems and fought a lot. It is amazing that we haven't stayed broken up though we have broken up MANY times. Not counting that we have been together almost 4years now. It seemed love was enough. Things have been way better this past year we haven't broken up once. BUT lately since he has stopped smoking weed and drinking things have gotten out of control. He gets mad about almost everything I say. It won't even be a big deal like I will ask him why he did something and he will start to scream at me. There is no way to stop him once he is mad he will scream or ignore me until he stops being mad but while he is angry he is very mean and malicious he will not accept reason or listen at all. He has very little empathy or regard for emotions in general but when he gets angry it is to an extreme... he doesn't care if I am crying at all. Aside from that he has always liked to be rough with me during sex. A few times he wouldn't stop even though I was crying and asking him to. Recently because I thought he was getting bored of me (i found out he watches strange porn, that of pregnant women being anally penetrated) I told him I would let him do whatever he wants sexually. He did, made me give him oral, ****** me in my vagina til I was screaming, anally penetrated me and made me cry, he choked and slapped me. I cried because I have been raped before and that is what it felt like. But the next day I asked him to do it again and he freaked out and didn't want to have sex. He said it was weird that I wanted it and after we fought and things were okay he told me he thought maybe I liked it when I was raped... Well since then we have had a lot of sex but he has only *** once, when he was being very rough with me. About a day ago we got in a fight and he lost his temper. He went into his room and slammed and locked the door. I tried to talk to him but he ignored me so I asked him to give me my stuff so I could leave. He ignored me still so I started banging on the door as hard as I could. He finally opened the door grabber me by my throat and slammed me against the wall while choking me. He asked "Is this scary enough for you?" I am aware he had done this to a girl before me but didn't think we would to me. His family has a history of bad tempers. I fear he has a psychological problem. I am sort of scared but I can't leave. I feel I have done worse things to him, I have rapid cycling bipolar disorder and he deals with it. I would feel like a hypocrite if I left not only that but who else could put up with me? I know I should leave but I have never been able to before, even when he cheated. I can get to the point where I say I am leaving you and he will say ok but I can't get off the phone or stop txting him... Even when he leaves me I will try to talk to him til he comes back or he will eventually start to ask for me back anyway. I don't know how to get out. PLEASE I need advice.