If only somebody would have told him that leaving once you learnt everything you could is a nice idea. But we don't seem to get such lessons, but rather have to learn them ourselves, right?

I wish I could believe that but still... in retrospect, it seems you are correct.

I don’t claim to have all the right answers, but I am a psychologist, and I have spent many years learning how to not think. All of the errors, mistakes, and failures in my life can be viewed as lessons I was always supposed to go through. A perfectly positive attitude charms our brains into properly regulating our internal physiology. Anxiety and the other negative internal states (mania, depression) typically can be cured by changing our internal dialogue and our perspective. One thing is for certain: you and I didn’t make this world. We didn’t invent people, trees, viruses, or love. We are part of a bigger picture. I compare it to being an actor in a movie. Why critique the scene? Why look back at previous scenes and wish they were different? Why hope for better scenes in the future? The script is perfectly written. Just read your lines. Play your part right now in the current scene with all of its ups and downs.

Prioritize your health. Go your pace and accept the consequences. Always feel satisfied with your choice.

I suppose my biggest issue is actually accepting that reality might not be as malleable as I thought. It's an extremely hard thing to accept even to this day (and I am hitting 41 y/o very soon).

Prioritizing your health is an absolutely sound advice every time. I started doing that and even if the improvements are small and hard to feel just yet, it still feels great to feel better than two weeks ago.