It made ME cry, that shit hits way harder than you'd expect. Don't worry, they'll be fine long term, though.

The fact they were a big factor in the divorce + him quitting his job at Trinity to go teach in a college because being around Lynn all day long is excruciating

She doesn't report him, and he stops going for teens after the divorce anyway.

The difference is history and circumstances. For the Kate AU, you have to keep in mind Cy never met Lynn in college, didn't become as socially developed, and key point here, never was introduced to kink. Even if Cy has a pretty strong libido across most universes, the reason he starts cheating on Lynn is because they were doing chastity kink play and he got frustrated at the fact denying her meant denying himself too, in a way. This version of Cy isn't kinky, doesn't see cheating as a "game" between Kate and him, so when she asks him to quit sleeping around if he wants to go steady with her, it's not a very big demand— they're not in a D/s relationship! As for the Divorce AU, it's less that Lynn threatened to leave, and more that she just up and decided to leave one day because Cy wasn't taking her emotional needs seriously, the cheating was just one part of it.

While Mac and I have played with the idea of her also getting with Cy because it would be very funny, ultimately for dramatic purposes she doesn't fit in that AU. She'd probably be off somewhere getting therapy, somewhat reconnecting with her mother and probably getting herself an OK Dom after looking for a while.

She removes it and gives it back to Cy, as a keepsake. He definitely doesn't feel extremely emotional about it.