I'm still boggled at how the writer is reaching the conclusion that this "is probably a three-way," unless there is vastly more evidence to support this than contained in the letter. Newsflash: as people get older, their networks shrink. Family die, friends die. Those who remain often become very close, because the pool of people who remember their younger years grows smaller, and because as their bodies age they're more aware of their physical interdependence with others.

My grandparents have a couple of very close friends. They vacation together. They invite them to all the family holidays. It has never occurred to me to wonder if they're swinging; I just assume they appreciate having someone around with whom they can reminisce about the Roosevelt era. (And if they are swinging, it's certainly not any of my business!)