professor nanami keeps his eye on you all through class, flirting with the sweet, pink haired boy next to you. he watches you tap his fingers with a pen to tease him, watches the way you tilt your head and smile as he goes on about the last game or other. itadori is nice enough. the sort of boy you'd bring home to your parents and, despite being a part of a particular crowd, he seems to take dating very seriously. that doesn't mean that nanami hates watching you flirt through his entire lecture.
his feelings aren't appropriate. nanami knows that. he knows that he could jeopardize your education were he to act on them, but it's one thing to swallow down attraction and another entirely to try and swallow down jealousy. so nanami keeps his eye on you, holding back your last exam paper. you missed a few questions and may need to go over them with him. that's all it is.