I'll answer rhetorically:

- It does not get easier. I can't imagine trying to do more than just this one thing.

- Your relationships do not get lower stakes or lower pressure. Much more of both.

- Once you've intellectually explored the problem, you're still obligated to graft the business onto it.

Are you sure that's what you want? Sounds like a resounding no. I think you should step aside and let the other co-founders use the equity to find someone with the skills.

The heuristic should be 'I want to work on this for 10 years with all non family waking hours whether or not it works' not 'I may feel like working on it 40% of the time or not'