I could be trying to go to college, work full-time, have 6 kids, train to be an olympic athlete, learn to be a master of 26 different musical instruments, write 16 novels in parallel, and then say: "I'm feeling burnt out".
The real problem isn't being burned out. The real problem is why you think you can do all of that and NOT be burned out. Why take on so many things?
I think it comes down to greed. You want it all. But basic economics says that you cannot have it all. If you don't find too many people trying to help you while you're trying to have everything all at once, it's probably because nobody really likes people who are that greedy.
If I was in your situation, I would get rid of my full-time job, get a divorce, make sure the kid goes to the mother with the divorce, stop exercising, get rid of friends who arn't related to my start-up, and forget about sanity. Sanity is for conformers.
It's kind of like a hoarder collecting so much junk that he can't let go of, that the junk weighs him down. You have to prioritize, and live with the necessities. Which is more important to you: your family or your start-up? And can't say both. It would be like saying I want to keep my $20,000 AND get that new Car. Well of course, everyone WANTS both, but that's not how the world works. Nobody WANTS to make sacrifices.
But you have to make sacrifices. Nature will sacrifice something in the end for you, if you don't want to decide. Your health will deteriorate, or your family will be troubled, or the start-up will fail. If you don't choose, something will be chosen at random for you and you probably won't like the result.
I'm not really making any suggestions to you, as your situation has many details I don't know about. But I ask you to at least consider whether or not you are simply desiring too many things and being stubborn about seeing reality.
The most important adjustment to make is to set expectations that allow you to do less.