I wonder, would telling him about my experience, and how therapy helped me, maybe make him feel not so vulnerable around me since I went through something similar? Or would telling him bring back too many of his bad memories and be more negative?
I would write him a letter. Print it on premium paper. If you have good handwriting (I suck) then write it out. Tell him about your experience. Tell him that you have some idea what he feels. Your experience is different but was similar in how destructive it could be. Tell him that while he says that it "does not affect him and it doesn't need to be discussed" he knows that that is not true. It has and it does effect him. While he may not want to discuss it with you, and you will not bring it up if that is what he wants, but that he still needs someone to help him with this. It will not go away.
I would include a book on CSA. Victims No Longer (Second Edition): The Classic Guide for Men Recovering from Sexual Child Abuse is my first choice. There are some other good books I read but that is one of the better ones. Have a look a http://www.youtube.com/watch?v=Nnp4MQ5I5Ss
I would not yet suggest a therapist because it may be too much and too threatening to him. Like you are backing him into a corner. Giving him the book with the letter may be too much also. You might get the book, read it yourself without commenting on it but so he will notice, and leave it out so that he might pick it up.
Build yourself a protective shell. Do other things that don't revolve around him. Do what you can that can help him but don't get sucked into the abuse any more than you have to. Do you both go out and have fun anymore since the disclosure? If not then try and change this. If not both of you at least you.
Learn what you can about CSA. Both to help him and to protect you. Recovery will take time and will be difficult.
So the above is what I would do. What you should do you have to decide. You are in it and you have to live with it. Whatever happens I hope things work out for you and him.