I know some people are worried about this going the typical route with female side characters but this seems to be going in a different direction.
It seems pretty clear that she isnt some irrational homophobic character. Instead it’s clearly implied that this girl has faced some sort of struggle during her time in city and is now projecting her issues and fears about conformity (an issue that is magnified in a culture like Korea’s which is VERY homogeneous) onto Mr. Kwon and his relationship.
The narrative isn’t trying to villainize her but rather show her for what she is: a young person with well meaning intent, but also someone lacking the perspective to understand that what she’s doing is invasive and wrong. I’m actually excited to see where her character will go and how it (hopefully!) develops from here even if it is in the background.
In case anyone wants it! https://www.novelupdates.com/series/the-guild-member-next-door/
he dies at the end (stepdad), and really pathetically too the whole story just gets worse and worse as it progresses. There's a sequel series that focuses around the little kid after he's grown up where he gets with an airheaded salaryman and that one is a lot more tolerable but still shit. This author has a lot of works with children in sexual situations so just steer clear of their stuff in general.