Exactly, I don't understand the hate against Junseo ? What did he ever do wrong except not realizing someone else's feelings towards him ? Like seriously that's just how he is, I know dense people and it's not like they do it purposely (is it frustrating ? yes but nothing to blame them for), they often don't see why people would like them so it never cross their minds.
He dated that girl because she confessed upfront not because he realized her feelings on his own.
Yohan's hate and anger are unjustified and just caused by jealousy and I'm pretty sure he knows it, I just hope he'll apologize one day and make Junseo smile (Junseo seems to really like him even with how badly Yohan treats him). He looks like a puppy every time Yohan rejects him.
A lot of people hate on Junseo but he's actually a good guy. It's really not his fault that he was so ignorant of Hyung and Yohan's feelings towards him. I felt really bad for him in this chapter, because you can see how hurt he was by Yohan's words.