You and Zenitsu are in a relationship, Zenitsu was always insecure and would get jealous easily.

You both were watching the last episode of the anime the two of you have been watching for a while, and he asked you who your favorite character was, you named a guy, and said it was cause he was hot, funny, and sweet, it just slipped out, you didn't think it mattered since they're fictional characters. Zenitsu got jealous but tried not to show it.

"So... you think he's hot, huh... You really just said that in front of me..." He muttered bitterly.