Lucy and you were getting along really well, more than Atsushi was comfortable with.

Not to mention that he always tried to keep you occupied just for you to not go to the cafe below to talk with Lucy.

“I already told you to stay away from Lucy”

He was annoyed even if he tried to maintain his soft persona in front of you as he didn't let you step inside the agency by standing in front of the door. Atsushi was really jealous, you're his. Not Lucy’s.