I think I feel your pain. I don't want to highjack your thread so I'll keep it as short as possible. I've worked in my job for over 25 years now. I've been going "downhill" for years but I didn't know what to do about it besides get up and go to work everyday and suffer through it. I have bills to pay, after all. I finally realized a couple of weeks ago that I've hit "critical mass". I can't take it anymore and my burnout has burnout. All I am doing is throwing gasoline on the ashes to try to make it work. It's not.
So I finally talked with the boss (owner of the company). He won't let me quit either. We are trying some changes and see if it helps. We are reducing my customer account load, trying to cut my hours back (from 47 to 50 hrs per week to 35 to 40 hrs per week), and overall try to reduce the stress load.
Nothing could change until I said something. I did want to quit, but I was crazy scared to do it. But something had to give or I was going to have a serious meltdown. I still might. We have to see how this goes.
You need to do something to make a change. Let them know. If they don't understand that burnout is serious, then you know you need to leave.
Your sanity and well being is what is most important here.