You need to do what is right for YOU, I know it's a tough situation, but self-preservation is so important.
Maybe somehow or someone here can help you prepare what you want to say or a way of putting it when you tell your present boss.
Indirectly, it is sort of for health reason(s), after all stress does not only have the ability of derailing us, but also makes the body physically ill in different ways, even weakens the immune system,several legitimate reasons for having the need to switch careers.
When a job starts interferring with our well being, it's time to move on.
I wish I had more to offer, it's been years since I was in a similar situation, and it's all foggy, but I did feel so much better, mentally and physically when I moved onto another job from one that really was getting to me.
All I know it felt like a huge weight was lifted off of me after I gave my "goodbye" notice, of course it was on good terms, I do know it probably wouldn't be if I stayed there longer.
Take care of yourself, and keep in mind it will be all in the past in time. Today becomes the past,tomorrow becomes the present and so the cycle continues.
I'm wishing you so much luck in whatever you decide.

Take care,
DE