Don't Ask Don't Tell

My first wife Cindy had a lover who was the husband of a couple who were also friends of ours. His wife was also named Cindy. They had a Don't Ask Don't Tell (DADT) arrangement. Having a wife and a lover with the same name must have been very convenient for him.
It was so awkward for my Cindy and I though. My Cindy and he, my girlfriend Mary and I would go fun double dates.
But, it felt icky to me like we were sneaking around. His Cindy knew he was seeing someone else but not that that someone else was my Cindy. I considered his Cindy as a friend. I left it for them (he and the two Cindys) to work out and it didn't last long. We went separate ways.
I prefer to be open and for all parties to know. I do not like DADT. But, what if your metamour is in a DADT and that's fine with your partner?