I know I am an exception but I actually take some comfort that I wasn't thought of. My H was a master compartmentalizer and his LTA was in his "work" box. He kept it out of our home and family and our M, at least in his mind. I didn't even notice a difference.
He never made an active "choice" between us, in his screwed up world. He says if he had it would have been a no-brainer. He just kept the two apart.
It is a messed up way to live and he is now much more fully integrated as a person.
But, for the most part, these nasty cases of infidelity are not about the BS at all, rarely about the AP; truly about the WS and their issues. I find a degree of acceptance when I realize that.