If you have a family, wife/kid(s), etc, and you're looking for "balance", maybe the compensation isn't worth it. But maybe you have a mortgage and having the income is very important regardless of how hard you're working. Doesn't sound like you have the above pressure, because you'd probably would have never taken a job in a startup in the first place.

You're single (maybe not) but renting an apartment, saving a little money while you work... get the hell out. 70 hours a week is only worth it if you have equity or are well compensated, which you said you are neither. Also doesn't sound like you're working on something you personally believe in, otherwise you wouldn't lodge your question in the first place.

You know what to do. Good luck.