I had a very similar experience to yours (with the exception of partners and investors). I was building a staff scheduling system, launch with beta testers who tried it out and then suggested they'd start using it when it had feature x or y. I'd implement feature x and then they'd say they'd use it when they had feature z.

I came to realize that the challenge is in the changing costs. They already had a product that could do more than what they could do with the systems they had at the time (mostly excel). It did a bunch of reporting and shift swapping etc. etc. but there was no way it wasn't getting momentum.

Thing is, I just wasn't passionate enough about it to make it a product I would love working on for the next 10 years.

A few people here say you're burned out, maybe you are, but maybe there are other projects you're more passionate about.

The project I'm currently on I'm not madly passionate about as a product, but other people love it, and it is fun to move the levers and see the affect on traffic and the (potential) business.

You're definitely not alone in your thoughts on this one, I can appreciate where you're coming from. Hopefully you look back at this as a great decision.

Better things ahead!

(great writing style btw)