@relic626 - bull shit. Every girl I ever dated had a "celebrity crush" or loves their dad. Thats beside the point - "feelings"? She does not KNOW 100% that he does.
Yea, you don't seriously date somebody who is trying to get with somebody else - but MC isn't trying, he does not even think about it.
Something like that is EASY to forget once you balls deep in somebody else, girls make men forget about their lovers all the time - its fun for some to "steal". MC has no idea about his feelings ( they aint real, they don't exists, he isn't in love with any of these girls anyway - Kaoruko is just pretty and tempting and always teasing his dick hes thirsty and she offers massive benifits as a PIMP its impossible to look away its lust )
If you love a guy, but hes looking someplace else every once and a while - its easy to distract him with a little bit of effort. She didn't try - she gave up after 1 invite to move in together.
She dropped him way too fast, completely gave up. Why? because he didn't sex her a bunch? because he didn't jump at the idea of moving in together after 2 months of dating?
She ran away even though she had every chance in the world to get this MC to forget the whole Monogatari project - because the author needed it to continue.