I think it is because he doesnt really know how to react to this kind of situation or to rejection and hr doesnt really understanding that he is making yondeok uncomfortable too... what i see from the way that his mother treats him and his father too the family situations and the way that he is thw only child that is really being abandoned in the family even they still live together and it was of course his fault that he mistreated yongdeok and how he acted he was total asshole... and yongdeok too hurt a lot because of him and i wish that yongdeok should just firmly say that he really doesnt want anything with him anymore and he doesnt have a feelings to him and he should stop what he is doing right now but on the other hand if he really tell like this i dont think skyler will going to accept it pretty well too... but yeah this manga is really complicated one...
The "hate" is mostly how persistent he's being after the rejection, and it's not even really hate. It's just hard for me to root for him because of how obviously uncomfortable it makes Yeonduk. Like, at least give the poor boy a little bit of space after being rejected.
But I love the process of his whole 180. He reflected on his actions and is really trying to treat Yeonduk better; he gave Yeonduk an apology and clearly told him his feelings. Trying to avoid any more misunderstandings. ヾ(☆▽☆)
Now he just needs to work on being so... forward... and clingy. (⊙…⊙ )