~sigh~ here's my long story that I desperately need help with...?

Alright, I'm 16 years old sophmore, and my girl friend is a 14 years old freshman in high school. We met in October this year at a football game. At the time my best friend liked her, but I had an interest in her regardless yet told no one because my friend had 'called dibs' I guess you could say. Well, I told him I would help him get a girl friend, and since he had his heart and mind set on her, I helped him out. Eventually the two of them got together. They dated for a week, yet they never really seemed like a couple. He was always depressed, and she felt so lonely, and I discovered that she lived right down the street from my dads house. So me and her became friends and snuck out in the middle of the night to hang out. We had some good times, shared some special moments. And eventually we realized that we were in love and kissed. Needless to say, we both felt horrible, so we told my best friend what happened and this huge fiasco came about that lasted for a month or two. But finally, in on December 15th, when all the bad feelings were gone, she asked to go out with me, and I readily and eagerly accepted. Days went by, which turned to weeks, and eventually I had my first real high school relationship that lasted a month :) I never felt so happy in my life because I seriously risked loosing ALL my friends for her because I really do care about her and love her with all my heart. But the more we snuck out to see each other, the more information I found out. Her past is not a good one at all. Her mother was, and I hate to say it, but a crazy, drunk, crack head who had with multiple guys, had several children with different fathers, then abused them and finally left them all with their individual fathers. My girl friend had a younger sister and two older brothers from their respective father, who was also out of the picture, so they spent three years together in foster care. Her brothers were adopted, which left just her and her little sister, and eventually after a really long court case, her dad got them back. Unfortunately, after all the trauma he has been through in his life ( abuse, , crazy mother of his children, etc.) he didn't turn out quite that good. He abused and still abuses my girl friend and her little sister, eventually sending the little sister away and had her adopted to, leaving just my girl friend in his 'care'. He hits her, bashes her head into things, yells at her constantly, and flips **** at everything and everyone, and he's been doing it for years now. Because of this my girl friend doesn't have ANY friends at school, is bullied at home and school, virtually hated for no apparent reason by everyone, and has gone through 12 terrible relationships with guys who lied to her and tried to have with her. Even during when we met at the football game she was with a guy who was a drunk and constantly abused her too. So we've been dating for over three months now, our four month anniversary will be April 15th. Through these months I noticed I've been progressively becoming more of a pessimist than the optimistic person I used to be. I think the reason behind it is, as I was seriously just recently told, when my girl friend is abused by her dad, she becomes depressed and starts taking it out on me when all I try to do is help, and since she takes it out on me it gets me depressed, and so on and so forth. Already she has cut herself numerous times, but that stopped. Our relationship has been a strained one at that. She was a druggie for 6 months, and I used to drink now and then, but when we got together we made a pact to stay sober, which I've been faithful too. However a month or so into our relationship, she lied to me and didn't tell me that she had done them once while we were together and even after that she talked about how tempting it was. But so far she has stayed clean, which is good. Another thing is she constantly brings up her various ex boy friends and talks to a LOT of terrible guys that I tell to back off, but she is desperate to have friends, so she tells me not to ruin it for her. A few weeks ago she wanted to break up with me for reasons I'm still unsure about, but we got past that, and the last major thing that was bad was there was a school dance that I couldn't make it too, but she went to anyway promising to not do anything regrettable. Sure enough I found out she grinded with some other guys and participated in a 'grinding train' where a bunch of people grind together while another person goes through their legs and is ed. Yet through all the terrible things she does to hurt me... I always forgive her and try to move on. I get people telling me everyday that we should break up (including my parents and her dad who hates me), and so does she. I stay with her because I truly do love her and just want to be there to help keep her safe and feel loved. I think she is just so used to the hate t