Assuming it wasn’t murder then he was in a sorry state to drive him to go to an outbuilding and kill himself behind a locked door knowing his poor parents would have to find him and deal with it.
So PTSD seems a plausible reason. Survivor’s guilt is a real thing. Whatever he was going through..it all became too much for him.
I agree with you. It’s all quite sad. And before someone chimes in with “ WHY DIDN’T HE GET ANY HELP”....the answer is that perhaps he never asked for any “help”!