Unless you were underage when you took the contract (or someone pointed a literal gun to your head) you were fully capable, should have known the the risks of the position when you started.
You took a gamble on a startup and you lost. You're not a unique or special snowflake in this regard. Brush yourself off, maybe take a paying position to build back your reserves, and maybe attack the next gamble with some more wisdom.
At least under California law, his legal rights may extend beyond just "brush yourself off." It is incredibly shmucky for him to not find out what he is entitled to.
You took a gamble on a startup and you lost. You're not a unique or special snowflake in this regard. Brush yourself off, maybe take a paying position to build back your reserves, and maybe attack the next gamble with some more wisdom.