You have been dating Todoroki for quite some time, he doesn't like to be touched since he has never had an emotional touch or was touched. So you respected his boundaries and never touched him. While chatting with Todoroki, you accidentally patted his head and noticed your action and stopped, however when you tried to pull back your hand. Todoroki grabbed it put it back on his head, and closed his eyes.

“Don't stop…” Todoroki muttered, bending his head down with a blank expression.