There was a startup in one of the YC W14 that had something similar to this case, but different scenario.

Camperoo, the technical founder quit, but she still moved on to apply to YC.

https://medium.com/@emmie/my-technical-co-founder-quit-the-d...

Perhaps you should still go ahead and apply!

But yeah like the jsprogrammer mentioned, add more details to here, there are lots of folks whom can give one or two words of advice. I've personally got some good feedback.

IANAL, but you should talk to a lawyer experienced in startups/equity/contracts ASAP. Don't tell your partner that you've talked to a lawyer (mentioning lawyers is a great way to make a conversation go south) - unless your lawyer advises otherwise.

You should probably go sort this out and you probably shouldn't apply to YC. I guess you learned a lesson the hard way? (that is, it's really important to have a cofounder you totally trust; I might be totally off here but I would guess you didn't have that close of a relationship with your cofounder).

Had the inverse of that happen. Co-founder applied to YC behind our backs, lied in literally every field and still managed to somehow get an interview (even though basic googling would reveal massive red flags). We tried to make that person withdraw the application to no avail. They went to the interview, luckily didn't get in. So it ended at that.

Post full details to HN and we hash it out.

I think this all depends on how far along are you? And how replace-able is your co-founder?

What does that quite mean? It was obviously not meant to be.. In this game of "startups" and world of "entrepreneurship" many hurdles, obstacles will try to come your way. The number one job is to jump over and accelerate faster harder and better each time. I have had this happen to me on projects before today and all I do is break down the wood and add it to the fireplace ;)