@Siquall I have this feeling that Hamin wanted to help but since she didn't understand anything about the two people fighting (like who was right or wrong, past history, etc.) she didn't get involved right away. She seems wise and measured in her actions and words even when she's coming off as cool or cold. She interjected right away once she understood not only the pattern of who bullies who but the fact that MC is so distraught over it on a constant basis. She is awesome.
Then, for the class rep (and this is only my guess), he heard from the stalker that someone came and tried to stop him from stalking Sugar (can't think of her name, close enough) and class rep put two and two together that the person who missed the movie also showed up on Monday with cuts, bruises, and bandages (literally the first thing he saw / noticed on MC). Between then and now MC and his "girl" have been appearing closer and he even protected her in dodge ball. Ever since MC beat up the stalker he's been slyly watching and gunning for MC like when he pulled that move in the dodgeball game to try and nail him unexpectedly.
P.S. when someone catches your throw in dodgeball they are out and MC deflected and Sugar caught it yet class rep was still somehow in the game when gym period ended.