When to quit (when I already feel like it’s the only way)?

Just listen to what your inner self is telling you. You don't trust the CEO, you don't get paid as you should, the business is failing and you're happy when not there. All the signs are there for you to move on. However, if you like the business and want to make it work, maybe you should be a co-founder instead. This way, it makes sense to not get regular pay because there's something else for you at the end. However, I would not recommend this because you don't trust the CEO ...

Just start looking for new opportunities. Once you get an offer you like from a different company you can decide whether to take the jump.

If you feel like there is nothing more left to learn. Jump ship. <em>I</em> He should be kissing your ass for staying. And if your in CA, feel free to report his @$$ to the Ca labor union for late payments

Thanks for your answers. I decided to pause for a bit, to see if any of the leads does result into something.

At the same time I will also make it clear that I'll only go back to work once I receive the money I am owned. I already worked for free for a few months in the beginning, so it would be foolish of me to repeat that process.

In the mean time I will start sending my CV to other companies, and if possible try the corporate environment to get a new perspective on work life.

Regards.

Get a job with a big company. F_ck working in a startup. The probability of you 'bagging the elephant' in stock some day is pretty slim. It's a numbers game and most people don't win. For the 'chance', you are taking a sub-par salary ... now you risk not getting paid at all. If your investors have bailed, and you have no customers, you are f-cked. Get out. Get a job in a large tech company that's already established. Always fun and there's no risk of someone stealing your scooter while you're at lunch ... because they're past that sh_t and you can't ride in the office any more. You're welcome.