partner was raped as a child

me and my partner have been together for almost a year now and early in the relationship he told me he was raped by a teacher from when he was 8 until he was 12 (hes 26 now). I want to support him as best i can but i dont know what to do or say.
I am only the 2nd person he has told, the only other person that knew was another boy that he went to schol with and the same teacher was raping him as well. they were close friends until his death early last year.
he still has nightmares a few times every night. I want to help him but i dont know how to. can someone tell me how to reach out to him? Tweet