> I've spent over 1200 hours designing and developing and have a very strong vision for the product.

> I think my co-founder registered an LLC, but we've never agreed and signed any sort of partnership/ownership/nda agreement.

OUCH.

Sounds like there's something worth salvaging though, so why don't you two try and patch it up - maybe try to find a neutral third party or something? I think it might even be worth your while to jointly pay some kind of person who is good at mediating disputes to try and help you come to some kind of agreement.