You'd be surprised what people will put up with due to subtle manipulations of people in charge, peer pressure (of others working similarly, especially if your boss works harder than you do) and the promise of future reward for slog now. It sounds like the working hours started out fine, with the emphasis on it being temporary, and then the realisation started to dawn much later that although they said it was temporary it was anything but.
I've been in a similar situation and didn't realise how badly it was destroying me until I was complaining one day to my SO and it suddenly dawned on me that this was not something I could continue doing.
In the startup world the carrots called stock options. Having been a consultant at a few dotcoms during the boom, I have seen many a developer work themselves to death because "their stock would be worth a lot" someday. Unfortunately that day never came for my colleagues.
Yeah. I was promised days in lieu, but these were conveniently forgotten or "unable to be taken" due to other, new deadlines. I'm actually surprised I got any holidays at all, apart from the fact that HR got involved. My boss certainly wouldn't have let me have holidays, and I was terrified of losing my job at the time so I didn't want to question it.
I've been in a similar situation and didn't realise how badly it was destroying me until I was complaining one day to my SO and it suddenly dawned on me that this was not something I could continue doing.