But class rep is right in a hand, Joonwoo became obsessed by Sungah, even if he has to kill himself to protect her, he would do that. But, we can "understand" his acts, he was in deep hole, depression, bullied, he was saved by a girl, Sungah, giving hom some interest and regards, all he needed since the beginning
In the other hand, class rep is crazy on his way, i think crazier than Joonwoo but he doesn't see it, like Joonwoo doesn't see consequences of his acts