I feel that my ex just wanted sex. How can I get over this?

We dated seven months and after six we had sex. I thought he loved me but he treated me badly for one month, dumped me when I was ill and then screamed horrible things to me on the phone. When people tell me I should have been more careful, I just wonder, how careful can you get? I waited six months, and before that I had known him for more than two years as a friend. I couldn't and I still cannot believe or understand that he did this to me.