It's so hard when you know, but the survivor has simply dumped the information on you and now can't talk about it. I was there too. Eddie's suggestion is a good one. You can give him the book and he can choose to pick it up or not when he's ready. Other than that, there really is no way for you to bring it up for discussion unless he does it first, and even then, a conversation just might not happen. He may be waiting you out to see if the proverbial other shoe will drop on him. It will probably take time before he realizes that it won't.
The fact that he told you at all speaks to how highly he must think of you and that's a good thing. Keep being his friend and his confidant when he needs it. Being a friend is a wonderful gift; I think it's the best thing you can do.
If you fall down 10 times, Stand up 11.