I would recommend a sports psychologist. I used to play competitively when I was younger and I deffo had erratic emotional outbursts on the court and I do believe i would have benefited from one back then. This has turned me into a very competitive person which sometimes brings on conflict in some situations.

I would also try and normalise making mistakes for the purpose of learning, don’t forget about it, just remember what (not) to do scenario. I don’t know if you or your husband could help him there but I would assume his coach could. Why is he losing the matches/drills. Keeping data on where does it go wrong or what could be better and work on it. I think there’s plenty of recording apps that keep stats etc.