That's good news that he's getting treatment. Take that to the bank. I have a better idea now of what's going on for you.
Consider the possibility that the "getting worse each day" is part of the healing process. It does get worse, in a sense, once you start dealing with the issues. Being conscious of the multiple facets of PTSD blows out any other thoughts and feelings you have, sucks every ounce of energy you have, and overwhelms your tolerance of outside stimuli, including loved ones.
It's entirely possible that the reason he's unresponsive and literally and figuratively remote is because he's mentally busy. Therapy and recovery can be absolutely exhausting to the point you just want to sit and mentally fight the battles going on in your head. Anyone coming along wanting to interact can be irritating.
I hope this makes sense to you. If you don't mind, my advice would be to offer encouragement and to let him know that he can reach you when he's ready, on his terms. For now anyway. Try to see this phase of his recovery as positive, though I know it sure doesn't look like it.
I know that puts a strain on you. Hang in there!