"Eats well" can mean a lot of different things - I would highly recommend checking out "the whole 30" and primal/paleo/low carb diets. Five years in, it's still on of the best changes I've ever made in my life - many accounts suggest it improves testosterone levels in men too. I was never fat, and I certainly didn't think that I was particularly unhealthy or moody or numb to what my body was telling me, but changing my diet greatly expanded my awareness.

Otherwise I'd say this really sounds like an emotional problem and therapy would probably be helpful. Putting pressure on him and saying you need sex to happen at least this often might not be helping the situation either. It sounds like he has some major sexual hangups and lacks the ability to communicate his needs surrounding the issue.

I'd recommend looking into the Adverse Childhood Experiences study - obviously it's not directly related to sex, but it can help identify root causes in a lot of different places where people might be struggling. I was introduced to it through a series of episodes in "The School Sucks Podcast" (the name doesn't do justice to the level of discourse). I think their commentary does a lot to expand on the shortcomings of the study and the ACE test. But the general problem is that people have very little awareness of how experiences in their childhood impact them in lasting ways because it all gets normalized - basically it's all they know so there isn't anything to really compare it to. There is also a tendency for people to block out and downplay significant events in order to lessen the pain of having to really face or re-live them and all of the implications that might go along with said events.