Maybe let him have his space? If he isn't coming home drunk or high and causing problems and if he is attending his therapy sessions, I wouldn't worry too much about him.

Some people NEED time to themselves or they can't function. It's nothing against you and it isn't that he doesn't love you. Some people are introverted and are. thus, wired that way. I would know because I happen to be that way myself.

Also, you might want to consider communicating your feelings and concerns with him in a more diplomatic sense rather than simply nagging him. It would work wonders in the long haul.