What you've just said does make things seem clearer.

I know it may sound odd, but have you thought of phoning a rape crisis hotline, and explaining the situation to them? I know that it's very unusual for a man to be sexually abused by a woman, but he seems to be showing classic symptoms of rape trauma. Even though they probably won't be able to help him personally, they might have contact numbers for men who have been sexually abused.

It's not surprising that he feels guilty and ashamed about what's been happening, and I'm sorry that something happened to trigger these feelings in him.