How do you get out of an unhappy relationship?

I am with a guy, and have been for about 5 months. Things have always been pretty rocky for us because of the constant problems that I have had with finances, and family problems. My mother couldn't afford to move my brother myself and herself into a new place, since we got evicted from our old one, and she left us here to fend for ourselves. Things have been tough for about two years with money, and we have been dirt poor, no food, nothing for that long. My boyfriend came into the picture knowing all this, but it didn't seem to matter at the time. Sooner or later, it did. He got fed up with how much I had to deal with, and how I would cater to my mother and brother like they were my children. He would take things out on me, yell at me for things I couldn't help, and make me feel bad about everything that was going on. I secretly wanted him to leave, so I cheated on him with someone I was still in love with. My ex. He ended up finding out and his obsessive ways started showing up. He had found out by looking through my files and folders on my computer, and he left my house only to return and scream at me calling me a and a slut and any other name. I was hoping he would just leave since I am too scared to leave him for fear of what he would do. I felt really bad about cheating on him, and for about a month I held it all in, and made things the best they had ever been. He chased my friend and I down the street in his car when I tried to get away from him because he was scaring me with the way he was acting [standing in front of the door, not letting me leave, saying horrible things]. I know I am in the wrong for what I did, but honestly, I thought this would be the only way for him to let me go, and just move on so I could be happy. I don't know what to do. Has anyone been in an abusive relationship before? I need advice.. I think I love him, but I don't think any amount of love is worth this pain and heartache. Please help.