My boyfriend treats me horribly but I can't let go?

I've been going out with this guy for almost a year. He was my best friend for a long time and we ended up falling for each other. The first few months were amazing, I've never been happier. But after all that, it went seriously down hill. I would find inappropriate texts from girls on his phone (which he would entertain) and when I'd bring it up, he'd shout at me and tell me I'm insecure and stupid, that Im trying to isolate him from people...to be honest, I felt as though he wanted me to find these messages, always asking me to read texts etc. He put a complete end to my social life..always fighting with me if I wanted to meet a friend without him (male and female) or he'd be so rude and obnoxious to my friends that it would just scare them away. When I have exams and I want to study in peace, he'll constantly nag me and tell me I'm neglecting him and that I don't love him. But when he's at work or out with friends he'll shout at me for being too needy and "suffocating" him. He also makes fun of the fact that I've been diagnosed with clinical depression. He tells me I'm crazy and that I'm lucky he puts up with the fact that I'm a "psycho" (not sure where he got that from) Anyway, everytime I try to break up with him he'll cry, tell me he'll change etc. He even threatened to kill himself a couple of times. I also feel kind of scared to break up with him as for the best part of a year, he's the only person I've interacted with-Im scared I won't make new friends and my old ones won't want me back after the arguments etc he caused. Please help me..I don't know what to do anymore. Thanks.

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