How can I make life better for my fiance who works 100+ hours/week and is burnt out?

I've been with my fiance for 8 years, living together for 3. He works in an extremely competitive industry and is very successful at what he does. I'm very proud of him and while, of course, I miss his presence, I'm happy to help him with the lifestyle his career choice imposes on our relationship.
Much like everyone in his industry, he periodically experiences serious burn-out, but is not in a position to take a career break or has no desire to change industries. He sits on his computer all day, gets little sleep, and is online basically 24/7. He can't commit to any plans (with himself, his friends, family or me) because they may (and mostly do) get canceled last minute. Not having any time for himself or the things that make him happy, naturally, takes a huge toll on him.
He is the unhappiest he has been in a long time. His health has gone down the drain, he is in physical pain or feels some type of sore all the time. I cook our meals, and follow a healthy diet in general but we drink, and he snacks a lot during the long nights he has to work.
My question is: how can I make life better for him? Small or big? To help him get through days or to help him embrace some small changes that can impact his health for the better? Any advice is more than welcome including to just leave him alone.


Source.