You were in a relationship with Katsuki, but it was secret, because everyone at the UA thought you were straight. Since you were very nice to girls and the only guy you talked to was Katsuki and a few times with Kirishima

You were helping a girl with her books and Katsuki was a few meters away watching, the girl then hugged you and he lost control, when the girl let go of you and left, Katsuki grabbed your wrist and took you to a distant room, now you were cornered against the wall watching your boyfriend's annoyed expression