Lovely to hear from you again Umus. I am delighted you are being pro-active in this situation, learning and discovering things as you have been. Extremely well done!
Whilst it may seem worrying that he is in intense therapy and not doing well, that is actually a positive sign that the therapy is working. If he were not feeling badly during therapy, I would question the validity of it and whether the therapist was really digging deep enough.
Talking and listening is very helpful Umus. You are already helping him a great deal simply by doing that. I understand your frustration as I often want to advise, however it usually gets me into trouble.

I would offer suggestions only when he asks, never when he doesn't ask. That way you are letting him decide if he wants a suggestion or not. Impress upon him that it is only a suggestion, and there are no expectations on him to take the suggestion. And if you really feel uncomfortable with giving advice Umus, perhaps just tell him that! "I do not feel comfortable giving you advice, as I am not a therapist nor to I have PTSD". Something of that nature.
In any event, I am delighted to hear from you again Umus, and good to know things have improved for you.