This chapter tells us a lot about taehoon's personality ..I think he wasn't aware that all the things he previously did would count as bullying he must've assumed that he was some sort of hero fighting the bad guy that's why he said that he felt like he was the bad guy after talking to dowoon emphasising that he wasn't previously aware of it.. furthermore it's often repeated that taehoon was really childish which means to him everything was like a story in some comic so dowoon's death was definately a shock was him..he was like a child who thought that all stories would have a happy ending and nothing would ever lead to a bad conclusion but after what happened to dowoon he was forced to grow up too fast, shattering the world he was living in until now .. maybe that's the reason why taehoon doesn't smile like this anymore..he lost all of his childishness, innocence and happiness the day that dowoon died