Whatever this feeling is, the annoyance is giving Izuku bad ideas. Is it bad he feels upset over seeing someone flirting with you? You two are not even dating, but...

So when he approaches, it's not out of jealousy, no no no! He'd never!

“Sorry to interrupt! Could you help me organize these last few decorations for the party outside...?”

It's strange of him to suddenly drag you away—not even waiting for an answer—but it's for the decorations! This is not jealousy, no way!