I feel trapped.

I want to leave my husband but I feel trapped. Two years ago I moved 500 miles away from all my family and friends to be with my now husband. Our relationship moved quickly and I got pregnant fast. Because I didn't have insurance, we got married so I could get his for the pregnancy. About a month after we got married, when I was 4 and 1/2 months pregnant he kind of forced me into a situation that I wasn't comfortable with. He made me have a threesome with my closest friend. I told him no multiple times and told him I was uncomfortable but in the end, it happened anyway. To this day he says I didn't say no and that I should have made it more clear. I did, he was drunk. He ruined my only friendship. In addition to this he wants to be polyamorous and I do not. He has bugged me about this since we got married. He wants to be with multiple women and I'm just not comfortable with that. This has been a source for many fights. Fast forward to now we have our 13 month son and just found out I am pregnant again. I want out of our relationship but have no where to go. I have no friends or family where we live. I didnt finish college, only have a minimum wage part time job and no support system. I know he would get custody of our kids because he has his own house, car, a high paying job, and a support system. The only reason I'm still with him is because I don't want him to have custody of our kids. I don't know what to do or where to turn to. I need help. I feel trapped.