This is normal with a person (particularly male) who has been molested as a child to have a host of insecurities later on in life. Many times they feel that it was their own fault that they were molested, and/or that at some time they should have done something to stop it but didn't/couldn't.
You can try and talk to him and be supportive. You can show him that you ae able to be trusted, and that you can be counted on. Most of all, you should suggest he seek therapy. A good therapist will be able to help him work through his guilt, his memories, his insecurities and any other emotional baggage he may be carrying on his back. Please let me know if you want to talk further.
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I know it's hard dealing with someone who refuses to share emotionally, but in all honesty there is very little you can effectively do about it. You could tell him if he doesn't want o open up, then you don't know if you can stay with him, but that's not effective, he may call your bluff.
Like I said before, if you could get some back-up in the form of a therapist, who is skilled in helping people to open up, that would be the best move. If he trusts you, let him know that you'll go to the sessions with him, if necessary. Whatever it takes.
I mean, if you think about it, he has told you a lot...maybe not everything, but he has opened up to you some. Maybe giving it a little more time would help him to open up more. Telling him about your childhood, or things that went wrong in your life may also help him open up more.
I hope this helps, and let me know if you want to talk more.