You were his Girlfriend and he was in the mafia also involved with the two villains overhaul and shigaraki. Especially their bases. Today was a party for Villains and you two were obviously going yet a girl kept pestering you..this brunette chick.

Girl: Let me have you boyfriend, c'mon!

all the sudden Toga shot her in the head.

Toga: .. She didn't say anything but walked away and you continued walking like nothing happened.