Exactly, everyone was saying he's always been like that when all he's done is literally help MC.
He's always been like that tho. His actions might have been sweet on the surface but the occasional times when we saw his thought process u could see how toxic, obsessed and posessive he was. Actually this discrepance between his actions and thoughts always left me dumb LOL. It might have started as a curiosity/ convenience at first but he did fall for Yeomin and man doesnt even realize he did. And tbh i can't say everything he did was to help Yeomin. He did it to have control over him , manipulate him more easily. Even when he brough Yeomin to his house, yea was a sweet gesture and all but go back and see what he was thinkin for real
Im sorry but the sudden character change makes no sense at all? He seems like a completely different person, I get it if it was that kind of story but it wasn’t. At first he was just shown as someone that yes may have not been in love with the mc immediately and it was just physical at first, he was still a kind and considerate person. All of a sudden he turns into a obsessive, clingy toxic one? Make it make sense.