I'm sorry but the "do what makes you happy" idea will knock you off your goal. Sometimes you will have to make hard choices and put your future self above your present self. This is not easy. It requires resolve and sacrifice. If you harbor the "I have a right to be happy" thought then it will be used as an excuse and you will fail. Buck up and take the pain. It is so worth it in the end.
Maybe we are using the word "happy" differently, but if your life choices are making you unhappy to the point where you talk about it damaging you in a quest to get to early retirement that's not something to suck up and take the pain. Personally I don't think there should be any extended "pain" involved in the Quest for FIRE. If there is I would suggest there is something wrong.
You can die any day so being unhappy now because you think you'll be happy later is a poor choice in my mind. Both because there may be no later for you and because if you can't be happy now there is not assurance you can or will be happy later.
If by "happy" you mean everyday can't be a birthday party.....sure I agree with that. I don't love work. I do it as a means to an end. There have been short periods where I hated work. But those periods were of limited duration. Work doesn't cause me grief or damage me. Neither do my choices that allow savings for FIRE. I could restrict my spending to the point where it would hurt. If I did I could be FIREd today. Doesn't seem worth it when I look at the totality of my life.
I'd also suggest that the solution for not being happy is not spending more money by default. It's figuring out the underlying reasons for the feelings and tackling them. Some of the solutions might have a cost [therapy, working fewer hours, etc...] but they also may be free [exercise, diet, learning coping strategies, etc...]
The way JayKay expressed themselves the situation sounds pretty serious and I would encourage them to spend time trying to make it better. It certainly doesn't sound like a situation where "sucking it up"is the healthy approach.