Part of the issue is that I think back to when things were not going well in my MR. I would look ahead to the summer-fall of 2021 as when I was going to pull the plug since my D was 18. A common (from talking to other people that are unhappy in their MR) plan that some actually end up following through on.
My brothers sister-in-law literally moved in with her mom the day after her oldest son's graduation party. Never looked back and now is engaged to a man very different then her ex husband. The "grey divorce" is on the rise and I think will only continue to grow as people live longer. It is my opinion that the institute of marriage will be obsolete in the next 100 years. Sad but true.