How can my BF fall out of love over night? I'm so hurt.?

I'm so confused and hurt. My bf seemed fine... we joked and laughed and I was his baby and then all of a sudden all he wanted to do was go out til all hours of the night with his one guy friend and drink. And spend all his time with him. And he got mad at my for everything and screamed at me and berated me and pushed me around. Then one night he didn't come home and I called him and he said he was sleeping at his friends house and when I got sad he said we were over. Now he says we are over and he just wants to be alone. He said he was lying when he said he loved me. I told him I'm so hurt and he doesn't care. I did so much for him. I cleaned and cooked and di all his laundry. I bought him so much stuff. And he tells me I was obsessed with him. II just don't understand how he can go from hugging me and calling me his baby and loving me and telling me I'm great to treating me like this and saying he wants to be all alone. I put up with a lot and never left him. When he got drunk one night and said I made him want to beat the **** out of me I still stood by him. But all he wanted to do is always be with his on guy friend. Doing everything with him and talking to him more than me. He told me I was not important, and I'm so hurt. I just want him back so much. We were together for 1 1/2 years. This week he went out and my phone died and I ended up in the hospital for a few days and couldn't get a hold of him and when I finally did he said he wasn't even worried about me. I just wish I knew what I did that was so wrong that he is being this way? I did everything he demanded of me and still I was no good for him. :(