BeingMe, I agree w/Bea and abuse victims do tend to shove the situation under the carpet and do not want to deal w/it. If something should happen to one of his parents, it may set him in motion to finally do something about what he experienced. I suspect he's always been one to guard his feelings and not really allow you into his life any more than he had to. Such a shame and what his parents did to him has harmed him.
I do hope and pray that he will seek professional help. It's his issue to resolve and all you can do is let him go to figure things out for himself. You need to step back and take care of yourself and continue on w/your studies.
Please take care of yourself.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.