I'm sorry this has happened to you. I hope it can serve as a warning to other HNers that companies are not your friends, and that it's never worth investing yourself like crazy in it as an employee. Any employer will throw you under the bus as soon as possible, and possibly has already planned that in the contract you signed. That applies to three person startups all the way to gigantic multinationals.
Enjoy your personal time, leave at 6PM, turn off work email/slack/anything and do things that make you feel better as a person.