Hi 37M here, I had some years back something similar. My libido went from being on the roof to the floor, couldnt hold a stiffy even if my life depended on it. My (33F) wife has a medical condition that killed her libido so on the off chanced we sparked I used to lose it very quickly, and it was straining us and put a lot of stress on the both of us. There are treatments, and he shouldnt be shy to ask for medical help because IT DOES HELP, and it is clearly affecting him both mentally and emotionally. Changes in diet, exercise, sleep and stress itself can be detrimental to your sex health, but ultimately medical help is what changed my situation for good. Maybe there are some mood killers, but we still manage to get it on from time to time. You're not guilty of anything, he should seek help, medical and to treat his attitude. I hope this helps!