Tinfoil is right. Don't be an enabler.
Unfortunately there's no simple answer to your question. Here's what I suggest. Get him the two books by Mike lew that I mentioned. There are other books about survivors of sexula abuse that you can find in the library or book store, but these two are very good. There are also a whole host of resources that Mike Lew lists in the back of Leaping On Mountains.
This might be a good first approach. Give these to him and perhaps he will see that he is not alone, and not a freak. That's what we all feel like at first and for a long time; freaks. We are isolated not only from out own feelings but from others as well. Perhaps in realizing that what he's thinking and feeling is not unique, he will be encouraged to open up some more.
On top of that, I would encourage you to talk to him and listen. Do not judge him, because whay you hear mught disturb you. But if you love him, your support and love and trust is what he needs to start down the right path.
But like tinfoil said, don't sit back and do nothing. That's the worst thing you could do.
Best of luck, let me know if I can help some more. You can E-mail me if you wish.