Curious if this genre has been tried. Fairly straight but titillating.
How old are you thinking? Couples in their 30s & 40s are easy to find, so I'm guessing you're looking for older than that.
Old guy with Alzheimers and a cheating wife:
https://storiesonline.net/s/10890/before-i-forget
https://storiesonline.net/s/10866/air-possum
Divorced at 50, starts a new business, has a heart attack, starts a new relationship, old wife turns up like a bad penny, etc.
Qhml1 has a decent age range for his relationahips.
Banadin had a story on here 'Ever and Always' where the male and female MCx start out in a nursing home with Alzheimers. They were part of a drug test that got canceled. They started unaging and getting their memories back. They sued the insurance company for fraud, and used the money to find a home away from major population areas. They started trying to figure out how to cope with the collapse of civilization, and wound up in a government program working on the same thing.
It is no longer on here, and I couldn't find it on Bookappy either.
Edit: I found it on his web page: ednelsonauthor