You can't be diagnosed over the internet so I'm not diagnosing you with depression. And it does sound like you have that. Things you used to enjoy not doing it for you anymore? Trying to handle it yourself and not talking about how you feel? Definitely, I recommend you talk to a counsellor / therapist / psychologist. I mean, you're already reaching out to the tech disapora for help ( Ask HN ), so take what may be a more effective and qualified step and talk to person whose profession is helping people.
Now I want to enjoy a vicarious "I told you so" ( since I didn't tell you anything ! ). I have however heard the advice said many times that before you startup a startup consider if you really care about it so much that you shall want to be doing it in 10 years. Didn't you think about that? Haha. Schadenfreude.
Or maybe it's just a case of "You need to love what you do, because shit gets really really hard, and any rational person would give up." Maybe shit is just really really hard and you don't love it. So, nothing wrong with you. Just your situation is sub optimal.
I don't know how this works, but if you can get your stock options ( if they've vested ), just take them, and to do the acquisition or not depending on whether that will net you more money.
Dude -- screw the duty to investors and employees -- take care of yourself. You probably never know how much time you have in this body, so do what you wanna do. Pull the trigger, since time is your most valuable asset. Why sink another 3 to 6 months ? ( Sunk Cost Fallacy ) -- just get out and be with your family. What if you try to white knuckle this, choose to be a slave to your investors and employees ( slaves ), "do the right thing", and your relationship with your wife frays, and you can't fix it...and you're in worse shape 6 months down the line?
Take care of your mental health. Fixing the company, finding a replacement, serving your investors and employees doesn't sound to me like it is going to improve your mental health. So do something that will.
And remember, depression is really just anger ( barring "chemical imbalance" believers -- sorry where does that imbalance come from? either you've always been nature / nurture fucked up, or you made choices that didn't work emotionally for you, and "chemically imbalanced yourself" ), turned inward on yourself, that you haven't found a constructive outlet to express. So work out what you are angry about ( maybe about this company, or something about this situation ) and work out a constructive way to fix the problem. You are a problem solver, right?
Working at Wal Mart, doesn't seem to me like it is a constructive solution. But yeah, talk to a professional. And are you dealing with some loss of a close family member or friend? That's definitely capable of contributing to how you are now. And it certainly pays to talk to a professional to help you through that.