@twinklecake
In no universe is "a girl you like dating someone who isn't you" all it takes to make something NTR. And it's not even clear he likes her anyway; yeah, he's clearly giddy about the thought of her having a crush on him, because he thinks maybe she does, but he's also been pretty clear about not being that into her.
And yes, it does have to be some kind of actual infidelity to be NTR, that's the whole fuckin' point of it.
It's one thing to dislike people who have a shit fetish if they're super vocal about it and try to insert it everywhere it isn't, it's another thing to be so upset about someone else's kink you start seeing it everywhere yourself and hating things that have nothing to do with it.
Netorare aside, I cannot wait for the chapter where she invites him behind the gym or something and he thinks "oh shit she's gonna ask me out should I turn her down????" and she meets up with him to say "hey I'm your new step-mom."