Please help!

The guy I'm seeing has a bit of an issue that I'm not quite sure how to deal with. He was raped by his brother at 13. It's made a huge impact on his sex life. He has avoided relationships for the most part simply because he can't have sex. He can't get hard because he always thinks about that awful thing that happened. I'm not sure how to help him if I even can or how to be supportive of the fact that he can't provide that side of a relationship. Any advice?