Without knowing him it's hard to say, though he sounds like my husband in many ways. In my case, all I've really been able to do is support him in ways that I know, show him I care at all times, and make myself available to him when he's home. I can't push him at all or he'll just shut down completely and resent the pressure, which makes things worse, but often he'll be willing to share little bits here and there just because he knows I'm willing to listen. Sometimes it takes months to completely decipher what's wrong, but I can pick up clues in many of the things he says and, with patience, it does eventually come out. Most of the time he doesn't mind if I ask a question or two, as long as I accept whatever answer he gives and don't pry for more details. It's not an easy process and takes a lot of experience with your significant other to figure out how to do it in a way that will work, and to figure out what the proper response is once you do know what's wrong.