Spoiler!
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Tbh I could be wrong bcs I'm solely going based off the pics since indint actually understand Korean but from what I see it unfortunately seems to be that
I don't think theyre actually a couple per say since it seems like eunchaes big bro wanted to break it off but the other refused to. And they definitely don't have a good ending bcs even in the end eunchaes big bro seems to still hate him. But it does show them continuing the sexual relationship they currently have and theyre pretty much always together afterwards. From what I could understand the creepy brother had basically been in love with eunchaes big bro from a young age and even after having sex with a bunch of others when he was older he still thought of him. There's also a scene in the last ch showing the creepy brother like buying eunchaes big bro a watch so idk if that means they're actually together or if he just bought that for him. It seems that they're more than likely are a couple or are hinted to be one. Luckily you don't see much of them tho but I'd wish we wouldn't have to see them at all but yk.
seme uke the brother.. literally everyone! also, his "family" can all go to fcking hell! I hope they meet their demise before the story ends