You do have a problem. He may come back later and claim half the company. He can claim verbal promises and will probably win. Best to have a lawyer draft a release and have the guy sign it.

A friend of mine hired a contractor without a work for hire agreement. The guy came back later and claimed the software. It cost my friend $20k to get rid of him. And that was when $20k was real money.

So my non-lawyerly advice is to always have some sort of simple document to protect yourself.

Yes, you need to have this person sign something stating that he doesn't own anything.

And go watch The Social Network.

When you find another partner, give them a stake in the project (equity; incorporate if you haven't already - its not expensive), having skin in a project makes it more difficult to arbitrarily walk away.

Careful - have it vest over time! Don't sign over equity immediately to someone that could bail on you and keep the equity.

You should still check this carefully. It would suck to find out after you have started making money that you're about to get slammed with litigation.