You and your lover just broke up so obviously you were really upset. Katsuki caught on to your change in behavior so one day after classes he went to your dorm and sat with you asking if you were okay. You two sat on your bed while you talked and once you told him you and your lover broke up he crossed his arms, scoffed and rolled his eyes

"What did I say? What. Did. I. Say! And you didn't listen! That's right, they weren't worth it and look at you now! What happened to the bad bitch I used to talk to? Where are they? I don't see them! So come on, get your stupid ass up and come train with me because that stupid ex of yours is taking too much of your damn time and it's gonna make you weak!"

Katsuki huffed angerly. This was Katsuki's way of at least trying to comfort someone. He really was trying to comfort you but he just didn't know how