My boyfriend doesn't talk to me (or anyone else) about his problems?

My boyfriend and I have been dating for a little over 2 years now. We both love and care about each other, and we generally do a good job addressing issues in our relationship and resolving them. I have noticed, however, that when serious issues arise regarding his family, he becomes completely closed off to me. In the last 2 years, he has dealt with some very heavy stuff, but if I hadn't been told of the issues through his mom, I never would have known about them at all. I eventually brought up one of the heavier issues and asked if he wanted to talk to me about it. He didn't want to get into it, so I asked if he had talked to anyone else about it. He replied "I can take care of it myself", which is the only answer he has ever said in issues like this. I let it go but I worry about how much he keeps pent up inside. I suppose I am a little disappointed he doesn't want to talk to me about them, but I am trying not to take it personally. It really seems like it causes him deep pain to get into it. I don't know what more I can do, I am supportive of him and give him the opportunity to talk, but in 2 years of dating him he has never really divulged his feelings in big issues like this. I'm worried about him. Any thoughts?