A redemption, male lead regrets hurting female lead

Just when Yeonduk thought he was finally going to be free of his tormentor (and family friend and crush, might we add), Seo Skyler – coolest kid in school – saunters his way into the same classroom. Skyler might look blessed (his sister’s even in a girl group), but he’s got some family issues that only Yeonduk can understand. Yeonduk is more than just star-struck, though, and when Skyler starts acting nice and walking to school with him, he can’t help but hope there might finally be more between

Doesn’t believe her and thinks she physically harmed her sister without listening to her side. This gets resolved rather quickly