Sometimes, the best way to accomplish your goals is to work nonstop. Sometimes, it's more productive to dial back and make a long, sustained effort. Sometimes, the thing you're working on isn't worth the effort, so you do something else.
No matter what you choose, I strongly recommend you talk to your buddy. Don't vent, but try to help him understand what you're going through. Tell him what needs to change, and be concrete. For example: Say you'll work 40 hours a week, plus one weekend a month if there's an emergency. If your requests are wishy-washy or open to interpretation, each of you will have different expectations. It will just postpone the problem.
Lastly, don't get too worked-up about this. Worst-case, you walk away and the project falls apart. The end. Nobody gets physically injured. Nobody's life is ruined. Everyone moves on to other stuff.
Remember: Nothing is ever as good, or as bad, as it seems at the time.
Actually, it seems like a major problem is if they don't have anyone to vent to. The fact that they're making an HN post suggests they might not.
The HN post is of course more than welcome. What I'm saying is, they need someone in their personal life to vent to about all of this, otherwise they're going to start making bad decisions.
I vent to my cofounders all the time. Sometimes its about the other (we always circle around the next day and have a more thought out discussion), sometimes its about my work or more general stress. Definitely helpful getting through those tense moments and back to work, I really appreciate another perspective.
This is my approach to managing a full-time job and being the technical co-founder of a SaaS product.
I spent 8 months working non-stop (12-14 hour days, 7 days a week). It was extremely challenging and I came very close to burning out, but it paid off in the end.
After we hit MVP and had 10 paying customers, I made a very conscious decision to move towards a long-term effort.
Today, I feel much more confident about my ability to continue doing what I'm doing long term.
Talk to your co-founders, but remember that at the end of the day it's up to you to look out for yourself.
No matter what you choose, I strongly recommend you talk to your buddy. Don't vent, but try to help him understand what you're going through. Tell him what needs to change, and be concrete. For example: Say you'll work 40 hours a week, plus one weekend a month if there's an emergency. If your requests are wishy-washy or open to interpretation, each of you will have different expectations. It will just postpone the problem.
Lastly, don't get too worked-up about this. Worst-case, you walk away and the project falls apart. The end. Nobody gets physically injured. Nobody's life is ruined. Everyone moves on to other stuff.
Remember: Nothing is ever as good, or as bad, as it seems at the time.