If Mine listens to Hiromi and abides by his request, then she's not really any better than he is in that context, in my mind.
She, and all of the other people who Nonoka, should be free to form their own judgments and act according to their own agency when it comes to how they treat Nonoka. Hiromi being a doormat is his own business; Mine owes him nothing, and certainly doesn't have to do more than acknowledge that he is indeed a doormat.
She proved as much when she told him to cut the pity party bullshit and asserted that he and Nonoka are in no way similar. So my headcanon, whatever else happens, is that she writes off Nonoka, spreads the word to the rest of the friend group as to what Nonoka pulled, and they all are left free to decide whether she's worth interacting with. After all, Nonoka decided that her ex was worth losing her entire support base up to and including her own parents. So it wouldn't even be a surprise if everyone ostracized her.
So if she listens to Hiromi and treats Nonoka nicely and forgives her for such cowardly behavior, then that's Mine acquiescing to being as much a doormat as Hiromi is in letting others decide her actions for her.
I get it's Sasuga's usual shtick to make her male characters this egregiously pitiful, but I really hoped this would be a case of him actually getting angry and lashing out as a result. Instead he's just turned inward and gone "oh woe is me I guess I deserved this" and it's almost insulting just how little he's changing as a character because of it. I thought this would be the point where he'd get fed up with continuously trying & failing at relationships because he keeps doing the same thing expecting a different result, but perhaps Sasuga Kei is not actually aiming for meaningful progression for these characters or for this story.
You can write a trashy melodramatic soap opera that still treats its characters like realistic people, and I'd argue the story would be better for it if they were allowed to do more than have the same reaction every time to bad shit happening to them.