I guess wisdom and strength in ample supply are required on this one. I'm really at a loss what to say or suggest. Certainly if your bf is in danger of being badly triggered he needs to be able to take care of himself in some way. Definitely suggest that he talk to his T about it. Some constructive suggestions could be forthcoming on that front.
In my opinion it would be well if he would speak up and ask for what he needs. He wouldn't have to say why he feels he cannot watch the movies, but I believe it would give him a real boost by being able to say "Dad, I really don't feel I can talk about it, but at the same time I don't think I can watch these. Can you trust me on this one please?" If his father is as kind a man as he seems to be that should be sufficient. Of course that may not be possible for any number of reasons, but It would seem to me if he could see his way clear to do it, it would be a big boost to his recovery. The T would probably know if that would be a good idea or no.
Like Rick, I wish you both blessings and peace.
Lots of love,
"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting 'Holy Shit! What a ride!'" ~Hunter S. Thompson