@Tcof: Except y'know, he ditched her when he got a job transfer? Even though she actually liked him then.
And from this page:
https://mangadex.org/chapter/571011/3
It seems whatever he did at the time of breaking up, it wasn't good.
Long distance relation? Apparently too much effort for him.
Heck even in his internal thoughts, he likes her because she's 'easy' and can't say no.
Dude is just an egotist who only like her because she is easily pushed around.