It's interesting, until I actually suffered from PTSD myself, I really had no idea what it was like to experience it. In fact I was blind I guess to the fact of how common this is in our world.
One thing I'd recommend that I really believe would help you is to understand what he's going through.
As a depressive/PTSD sufferer myself I realize that I not only take on an emotional toll but a spiritual and physical toll as well. Imagine being exhausted just to get up from the couch, or to wash the dishes, make a phone call etc. I've been there and I WANT to do something but physically I do not have the energy.
Also I know that sometimes I refuse to do anything that has to do with opening up the wounds (writing, talking, being around people who may ask) because that alone can trigger not only emotions but oceans of thoughts that fill up your mind and they are not pleasant to remember what happened. It's like living a nightmare 24/7. Sometimes I choose to do anything else that doesn't allow me to think. Give him chores that allow him to "think" about something else. Mind stimulating things.
Make him feel important and wanted. I know guys feel even more worthless when they aren't appreciated. Let it be sincere. I know for me, I've become hyper aware of when someone is handing out pity rather than actual sincerity.
Ask him what he experiences (if that's a safe approach). Also I found if I have someone disappointed in me because I didn't do something, it really hurts, and I spiral down again. Use lots of positive happy talk and find things that he does do well and compliment and uplift alot. Turn on positive music with uplifting messages that he can listen to. Go on walks together (being outside really lifts my mood) and I'm confident you'll start seeing a change. Also see if you can get the high sugar, high caffeine, and deep fried anything out of his diet it may help. Don't do it all at once, but the way he eats has a Huge impact on mood. Before my bout with abuse (situational depression), I permanently reversed my own depression (Chronic) with positive thinking and eating healthier. I really hope this helps and if it doesn't then I still hope that you find something that does. Healing though is going to be what helps in the long run, encourage him. There really can be an end to the pain. Keep going, you can do it, you both are worth it!