I wouldn't jump to any conclusions just yet. Men are funny creatures. Most are uncomfortable with admitting their feelings and talking about their past. Clamming up after opening up to you is pretty much the norm, from my exerience. He's probably feeling a bit vulnerable after confiding in you. Rather than doing the sensible thing and seeing it as good that he's talked to you he's probably just trying to readjust his defences a little.
Give him time, let him know you care and don't push it. Obviously, if you think he still has a problem and it might affect you, that's one thing, but if he's being totally honest then it's taken courage to tell you. If you really feel strongly for him and think he's telling the truth, give him time. In the long run, him being honest is a good thing.