Years ago, 1967, I came back from Aden, and went through something similar, no support then, these things were'nr recognised, but I fully sympathise and empathise with your families and your predicaments.
Luckily, I recognised what was happening, and went to see a Hynotherapist, he helped me to understand and come to terms with it, maybe your son can try something like that, but, be warned, he'll have this locked in his mind forever.
The best treatment, as much as possible, would be to keep his mind occupied as much as possible, and when he's at home, try to have someone with him, to that end.
My thoughts are with you and your son, a brave man, and in my book, a Hero.
Sorry I couldn't help more.