Believe it or not, my dad had a friend in that situation. They were married, got divorced, stayed monogamous with each other. They just didn't live together. I guess they didn't want sex with anyone else but they also didn't want to live with each other.
The only thing that's weird to me about this is, why divorce in that case? There's no law that says you need to live in the same domicile as your spouse. Could've lived separately and kept stuff like shared insurance benefits and whatnot.
It's rare, granted, but it is a thing. Unless they wanted to separate their financial lives entirely and keep getting down, I guess.