How am i supposed to cope..?!

I'm 15 and have an alcoholic dad who blames my ma and I for his faults and problems. I've been taking care of the house, my younger brother, and my education while my mom works and tries to support us best she can by herself, since I was 11. I got into cutting that same year and I've been on and off addicted to it since. I've had therapy, and medication and things got better but now my home life is just flat out horrible. Every day there is some sort of screaming argument at my house, without fail. My mom has threatened him we'll leave more than once but we never do because she feels responsible for him and is afraid of what he would do if we did leave. She no longer has the same feelings, and I have told her she deserves so much better but she doesn't have the strength to leave. I can't stand to be at my house so I try and stay away but it just comes back and hits me in the face everytime. I've threatened to runaway and it didn't do anything but freeze the moment for a day. My brother was diagnosed as depressed and that paused it all for a week. But now, its just routine for things to be crap, wake up act like everythings fine, and repeat. I just don't know what to do anymore. We've sent my dad to rehab but that made everything worse. I just don't know /: My mom has seen a few of my scars when I was in the hospital last May but she didn't do anything but get mad and yell at me. Which for a cutter that never helps. I want to tell her, and get help, but I'm so scared of being judged by her and completely disowned because of the way she acts towards things like that. I try friends, and finding those close friends, but High School has cost me all but 5 people I was once close to and I have no one to turn to, to confide in.