When you release your software for free you don't owe anybody a thing. If you're getting burnt out or it's impacting your personal life too much then don't be afraid to stop and hand over control of the project gracefully. The latter is hard to do for most people though, because giving up something you've spent so much time and effort on is challenging. However, your irl always comes first.

Burn out and stress applies regardless of whether you get paid for your work or not. Plenty of people feel the same way about their paid jobs too. I think all being paid to continue work on this project will do is prolong the inevitable, that it's time to move on regardless.