Why am I still with my abusive boyfriend?

I am 18 and my boyfriend and I have been together for 2 years. I honestly think I love him and I don't know why. He verbally and emotionally abuses me. He calls me worthless, ugly, fat, a hoe, etc. I don't understand! I'm not any of those things... I want to leave him but it's like every time I try, I can't bring myself to do it because I'm so attached to him. I guess my real question is, why am I in love with someone who treats me so bad?