How do I get out of this destructive situation?

My girlfriend and I have been together for almost 2 years now. Back in December up to March we almost had a baby (yes, almost /:). And then just currently I was caught with her camera, it had pictures of both me and her on it. As I understand these are some extreme circumstances it’s not my relationship that is destructive. But back in January, my grandfather passed away. And my mom got control of everything. I have lived 99% of my life with my grandparents, because whenever we move out and my mom gets control, she goes crazy with it. And so you can only imagine what’s happened since she got total control. When I say she goes crazy with it I mean it as in she “accidentally” choked my brother with his shirt. And she has kicked me and my sister out numerous times because she’s mad…one time she pulled me and my brother out of my grandparents house because she was mad at my grandfather and we lived in a tent for a week and then in a motel for a week. And one other time she got on top of me and started punching me till there was bruises all over…unfortunately I was so afraid that I waited for school to start up again to tell anyone and they said nothing could be done because there was no proof anymore. Though I KNOW it happened because it was so bad my older sister didn’t want to look and she tried covering my brother’s eyes. But ever since she got control she has been yelling at everyone. And it’s gotten to the point where no one can really stand her. When the pictures incident came upon us, three days after I was caught she gave me a punishment, that I wasn’t aloud to see her for a while. I was fine with that, parents are SUPPOSED to punish their children. Then for the next week, we had good talks. Not arguing. Good conversations. We had finally been getting along for the first time in about ten years. Another piece of information, my brother is ten. Besides the time up there^ she gives him everything. And really never pay even the slightest bit of attention to my sister or I. My sister now lives in Orlando, she is 18. But anyways. After that week I was in my grandmothers bathroom (little house bathrooms have good acoustics.) and she rips open the door and grabs my iPod, my phone, and then she went through my room and started ripping things out of the wall. NO ONE knew why she was doing it. Someone suggested “Maybe she found more.” But thing was there was nothing else. It was a one time dumb thing. And right before she stormed out she screamed “YOU’RE NEVER ALOUD TO SEE HER AGAIN!!” And then recently about 1.5 weeks ago I went to the doctor and he told her “He’s 16 correct?” “Yes.” “Then you really don’t have all that much effect on him. At this age they have a mind of their own.” “I know he reminds me this all the time.” (Which was a lie, because I always listen because kissing her a** is the ONLY way you get things in my house) “Then all you can do is guide him. But this “Never-aloud-to-see-your-girlfriend, and this pitchin’ a fit, and whining, is gonna do NOTHING but make everyone in your house miserable and PUSH your son away from you. You can’t control him, but you can guide him.” “But I have to do something!” “I understand that. When I was his age, I was caught shoplifting…my parents raised holy hell with me! Then grounded me. But they let it go. Corie….you have to let it go…” “Ok.” (that was a VERY pissed off ok. not yelling but pissed) “Now I also advise that you get some family counseling.” That was then. I was put on a mood mediator because I can get really depressed sometimes. And recently she threatened that if I don’t “change” she’s gonna take away my medications…and everything is just going bad…what do I do?