I would say this: it is never as bad as it seems and it is never as good as it seems. Startups are very hard on everyone, despite the smiles and glowing press. What you are feeling is natural, and a lot of close-to-founder employees go through it. (Founders do too.)

Tactically, at your age and at that level of comp, I would stick it out for a few more years or until it became clear that the ISO's were not going to be worth anything, which ever came first. Jumping ship almost always seems more attractive that it turns out to be in actuality.

I would also recommend some sort of stoic philosophy. I am a Christian, but there are plenty of other options: zen, greek, etc. At the end of the day, none of this shit really matter that much, and, additionally, it's all pretty funny if you can get some mental space between yourself and the situation.

Good luck.