How Is This Ok?

I have had a rough go at life from the beginning. My bio dad killed himself before i even turned two years old. For a while my mom was the sweetest person. When I was molested by my stepgrandfather at 5 years old, she did what any mother should do, protect me. When I was once again sexually abused by my brother, she chose to help me and him by putting him in foster care. He had raped me from the ages 9-13 and it was rough. He was the one person who I could trust with anything. The one person I knew I could turn to, and he took that away from me. He changed into a monster every night. The betrayal was the worst thing I thought I could ever experience. Or so I thought. I started getting into trouble, acting out. Getting arrested and running away from home, just to have one night that I didn't have to worry about the monster. So I could feel safe. The behavior gradually got worse. And when I told my mom about it, at first she called me a liar and sent me to my room. She Started hitting me and my brother. Well, that made him only touch me about once a week. So, it was almost like I welcomed the bruises and cuts because it turned him off. It helped me get rid of him at least for a couple days. I thought that was the worst pain I could ever feel. But how I was wrong. My mom has been married multiple times, each man physically abusive. Gradually getting worse as time progressed. my mom and I stopped fighting for a while, because for a short period of time there was no abuse. Then she got married...again. I hate him. He had started hugging me a little tighter and tighter till he wanted more. I fought and fought but there was no point, I was helpless. I thought it was all news to my mom and i didnt want to ruin her new marriage so I didnt say anything. Then this past new years eve, he cancelled my plans and I had to stay with him and my mom, to play cards. I drink a few beers and said I didnt want anymore. Then he told me that if I didnt drink anymore tehn he would hurt me but if I did then he wouldnt. So I drank shot after shot. Till I cant walk straght and go to my room. They both follow me in there and sit next to me. She started to talk to me differently then she ever had before, and even through my drunken stupor, I knew this was planned. As he continuously raped me throughout the night, she was there, telling him what to do, how to do it. Till she could get her turn. Thats when i figured out that what my brother did wasnt the worsr pain I could feel. The worst was when my mom betrayed me so deeply. How could she do that? She was there to protect me from bad people when I was young. Well, what happened. It pains me so much to recount this. But I need someone to know. I dont have anyone to turn to. Well, after that incident I started getting in trouble again and she once again started hitting me, so i got fed up and hit her back. The cops get called and guess who gets locked up? me. She had a bruise on her face said i started it and that my bruises were from her using self defense. Now I am getting waived to adult court for a felony. I am terrified and confused. I feel like I am that 13 year old girl crying because my brother is hurting me... but this is much worse. The betrayal of my mother allowing the things he did to me to occur, let alone join in and encourage it? How is this ok> How can this happen? I am 17 years old and am in so much tyrmoil. I am scared when he stays the night and I cant drink at all. This has affected me in so many ways.. its almost unbearable...