What's different in my situation is that my ex gf was extremely understanding (as it sounds you are, but maybe he doesn't know that as well as he should) and that I am (obviously) willing to vocalize my thoughts and emotions.

I think in your situation, just reminding him here and there that he CAN be open with you, that you are there to help and that you are not going to judging him will help a lot. It might still take him a long time to open up but if you do two things (again, this is just opinion) I think you could help your friend greatly.

1. Give him space when he requests it. Talk to him about what "breaking the barrier" might be for him. Let's say you just want to check in with a text every few days, ask him if that is okay or not. Find out what he means when he wants alone. Is it complete isolation or is he okay with some minor communication here and there?

2. Remind him you are there for him. For someone to talk with about EVERYTHING he needs to talk about and that you will not judge. I am sure he already knows this, but the occasional reminder can really help build trust if it is currently not there.

I guess I could add 3, never break his trust and keep anything private between the two of you. That is obvious, but worth saying.

I am really outlining what would make me happy in these situations, but it sounds like your friend and I have some similarities with isolation so maybe it applies.

This is kinda funny you posted this... right after I posted this:

http://forums.psychcentral.com/showthread.php?t=233907