I agree with Candu, help him know he is safe, wanted and accepted by you. You are NOT his therapist, so help him find a great male sexual abuse therapist and then let him decide when going to him/her is best, it may not the right time for him.
You are a supporter, which is limited to listening to him, having a sympathy, but not rescuing him by allowing bad behavior or abuse from him to you. Personal boundaries are paramount, as well as a support group for yourself in CODA(Co Dependents Anonymous). You need support. DO not take what he is frustrated about in the abuse personally. You are innocent, a wonderful human being, a beautiful, caring person. Always remember.
You and he can form a strong relationship through the fires of the abuse recovery, but there will be hardships. Make a plan that gets you from his potentially strong release of emotions or isolation to a healthy place for you and accepting this behavior as he heals. Consistent, long term support may be necessary.
A supporter is greatly valued here, Querida. Thank you for helping a fellow survivor. Please let us know how we can support you, and encourage him to find us and share his story do that he too may heal.