how do I deal with knowing he is sad and depressed and feels like his life is not living
You keep your expectations below zero. It is him who has to deal with it not you. Yes I know you want him back (I yearn for my H more with each passing day) but you can't heal him only he can do that for himself. All you can do is be there for him should he call on your help (and I truely hope he does).
Me 43 XH 45 M 2.7.88 Divorce 7.10.09 Kids D20,S17 & D15