This "too friendly" side character cliche in stories that have no real place in the story is ridiculous. Think about it, remove him from the story and it is better or doesn't dip in quality, because then the author is forced to create real social interactions/write interesting subplots between...
@Rozzak you're missing the point. If he wanted to say something about her relationship with a student, he should bring it up with her and let her make the choice. They're not even close friends, he has no right to pass that boundary.