How to leave a startup as a founder?

Just out of curiosity...You say there was no written contract at the start? If you wrote everything (or at least the majority of the code) and there's no written IP assignment, then you could conceivably _leave with the product_. It's yours, not theirs. Maybe. At least, the IP is encumbered by that fact.

I'm not saying leave w/ the IP, but you may in fact have a LOT more leverage here than you thing. You need to talk to a lawyer ASAP.

Practical elements:

1. Most founders end up putting a lot of their network/personal workflows on the company domain. Create copies/downloads/backups of everything so you have it. You can parse out what to keep once a termination agreement is formed. Shift your communications to your own email/domain or at least CC.

2. It’s challenging, but now is the time to shift to a “never split the difference” approach where you get really clear on the story your co-founders have, what it reveals about their motivations, and what they might reveal about what it is they really want. Chances are you a breaking up because they want different things than you do, that’s very useful in negotiating agreement where you win what you want without the cost of them feeling like they lost it.

3. If you’ve lost confidence in the business, selling your equity (or claim to it if you don’t already have an agreement on that) is very high leverage for you. They have to get it back if they want to raise capital in the future. No one likes ex-founders on the cap table except in very rare situations.

I’ve never looked back on a co-founder breakup and wished I’d put more energy into it. Get yourself a therapist/coach to help you let go of the struggle and put your energy into moving forward.

Good luck.

What would you do?

I would get a lawyer ASAP.