jak:
It's been awhile since I've seen it, but did they ever actually cheat?
They fell for each other, but I thought they stayed faithful to their spouses until they divorced. Though I felt bad for her ex-husband at the end. It destroyed him and messed up his ability to pilot a plane, but the wife didn't seem to care. I kinda wish she had realized she still loved her husband in the end and stayed with him personally. Even though she ends up with the other guy, it seemed bittersweet. She found happiness again by destroying another.
I'm in the middle of watching it now but
they definitely kissed, lied about their whereabouts and who they were seeing, stayed out all night with each other while making other excuses and fell in love. Emotional affairs are a thing too, and while every couple can define cheating in their own way and set the boundaries of what is acceptable in their own relationship, it crossed the line to a physical affair when there was kissing, sneaking touches to each other lovingly (on the plane, in the bar, etc)... and more importantly, lying about it.