Every single day. I think about it when I wake up, and I think about it while I lay in bed waiting to fall asleep. Biggest regret so far in ~40 years.

Well that's unfortunate. In this cabin dream, do you have a family or was your intention to live in a cabin in the mountains in isolation?

Regardless, perhaps make it a goal to do this when you retire. It will give you something to work toward and possibly quell some of your regret.

If it's on your mind this much, and I'm no expert here, you might want to talk about it with a professional. You can't let this stuff bottle up and eat away at you from the inside.