Being a therapist myself, I of course recommend therapy (that is if and when he's ready), so that he can work through this very traumatic experience... Then once he has started to deal with the sexual abuse himself, maybe you can participate in some counseling sessions with him to help you manage this very sensitive issue as well (i.e. intimacy). As far as your interactions with him go, I wouldn't push him to talk/disclose much, but let him know that you are there for him when he's ready. As for you, he clearly feels he can trust you very much, to share such a personal story. That in itself should make you feel good- he is comfortable enough to open up to you. Best of luck to you both.
P.S. In finding a therapist, I always recommend you find someone who has experience working with victims of sexual abuse.