Keep up with this story and more What was causing this emotional disconnection? It is feeling underappreciated and like they can't win—and maybe they do things that make it hard for her to appreciate him—that usually leads them into dangerous waters.
Appreciation is what they first and foremost get from the mistress.
I'm suggesting that you look at the signs that are going to mean the most and then do something about them.
Don't do what so many of us do, which is hold our breath and hope [the problem] goes away.
Was there something they could do to prevent this and create a mutually beneficial relationship?