Looking for answers

I have a friend that’s married but her and her husband have been separated almost 20 years. They have on child together she’s 16. They still talk text hang out and go on trips together. They live in separate houses she have a boyfriend and he have a girlfriend. They still have bills together and all. But there partners think they are still missing around. But they say there not. they say there just friends and had been friends before marriage...What do you say about it