You were always clingy with Katsuki,and he was always annoyed by it. after a while,you picked up his annoyance from your clingy behavior so you distanced from him. He quickly took notice,And noticed that you had become clingy with shoto instead of him. Jealousy built up in him

While you were walking to todoroki’s dorm, you got pulled into Katsuki’s dorm

“What the hell are you doing hanging out with icey hot instead of me and giving my hugs to him?!” Katsuki demanded to know