I want to leave my boyfriend but he has been through a lot?

I'm truly unhappy in my relationship and think about leaving everyday, but my boyfriend has not has his biological mom or dad in his life since he was a baby. I feel like I'm all he has because he doesn't have much family or friends but he doesn't treat me right. He constantly pushes me to my limit and thinks it's funny. He screams at me when he's hungry and I'm not moving fast enough to get him food. He gets extremely angry with me when I don't have sex with him. I want to leave but I care about him and I don't want to ruin his life.