Basically, the top just want the uke all to himself. And he doesn't get it yet, or maybe he's already on that part but still in denial accepting his feelings. 'Cause if he doesn't have a budding feeling to the uke then he's just a selfish asshole who doesn't one anyone dipping on what he deemed "his" .
SPOILER
I read ahead on the raws a little bc I know a little Korean and basically they’re fwb but he’s caught feelings he doesn’t like it when someone talks badly about the uke saying he’s already fucked him and slut shaming him and shuts it down. When he sees someone kissing him at the bar after he tells the uke to stay in the car that’s when he finds out and he’s distraught bc he realizes he’s been treating him “wrongly” bc he kept insinuating he was promiscuous then the uke puts him in his place saying what does it matter if I was a virgin or not gay before you only want sex anyway right. So I think the authors trying to explore the nuances of that.
so let me get this right, the bottom is a "slut" for sleeping around but the top isn't? huh?