1: First off, tell them you're thinking of changing work. If they even hint at you being "too bad to get another job" they're gaslighting you and you should run, if they offer a raise then it's probably half the raise you deserve. Because if you're the only web/mobile developer at this startup you're probably doing a helluva job.
2: Don't work 70-80 h/weeks, I've only done so at special times since my early career, and when I've done so after then I've been getting paid by the hour.
3: That brain-fog probably comes from the overworking, you're not going to be making clever decisions at that state. You really probably need some months off to get to a better state (the magic thing is, when it clears you'll brain will start to itch with amazing stuff).
2: Don't work 70-80 h/weeks, I've only done so at special times since my early career, and when I've done so after then I've been getting paid by the hour.
3: That brain-fog probably comes from the overworking, you're not going to be making clever decisions at that state. You really probably need some months off to get to a better state (the magic thing is, when it clears you'll brain will start to itch with amazing stuff).