I'm literally in the exact situation currently. It's a bad thing to get caught in, because as the dev guy, at this point you've invested way more time and effor

I'm literally in the exact situation currently. It's a bad thing to get caught in, because as the dev guy, at this point you've invested way more time and effort than he has. Take some time to think about ways to potentially switch up your business model so that you can start pitching your product instead of him. You know it better than anyone else anyways. Really depends on the niche and target audience, but if you become very vocal about what you do, you might be able to snag a few initial customers to get things rolling so you can then have some breathing room to make the right decision.