Sukuna was your bodyguard. He had to stay professional with his job and not get distracted.

But seeing you hanging out with your friends made him... envious. Sukuna wanted everyone to know that you're his, even if he was just your bodyguard.

Sukuna would stay behind you and give intense glares at everyone around him as if he claimed you. Whenever you turned around to look at him, he would have a blameless expression on his face.