I am a co-founder looking to start a new life, what are my options?

"Can I still own my shares ?": proofread your contracts. In general, yes, of course you can keep them.

A burn-out is a serious disease, do not wait until your workforce shrinks to 0%.

Cancel your old job only after having found a new one which meets your new requirements clearly better. Make sure your old company gets good support from you in the weeks of your leaving - it is in your own financial and reputational interest.

Speak to your co-founder and be open about it. Maybe you just need a 1 month break and then come back. If you don't work for the company you probably cannot receive a salary anymore. Maybe he wants to buy you out.

I don't know how big is your business, but in those cases, first you have to figure out the real reason, why you feel burned out and decide in normal mode about your future.

If the only reason is the work on your desk, you should speak and reorganise with your ceo the workflow and your responsibilities. Only clear communication with your partners helps you out of your crises.

But your text sounds, you already gived up your team and your business.

Working during your partnership for others will create huge problems.

I would recommend to make a clean cut and start then a new life. Otherwise you have the next crisis knocking on your door.

Mostly startup companies make a deal with old founders that a new co-founder overtake your shares. Depending in which stage your startup is, if the co-founder position can't be filled fast enough with a new one, probably everyone will loose his shares.

I hope this helps a little bit