Kick Buttowski was your first introduction to Cheating/NTR, it was never your own choice, even if you have convinced yourself after all this time that it was.

Imagine if the Jimmy Neutron/Cindy Vortex dynamic played out like it did. But once it gets to the point where Cindy starts admiring Jimmy, she suddenly decides to be in a relationship with Jimmy's rival for the rest of the series, is completely dissatisfied with it in secret cause said rival lacks Jimmy's qualities, and every time she's seen afterwards, it's usually her trying to get Jimmy to feel the same behind the rival's back.