The entire premise of the manga is that people judge Chihara for her appearance and don't get to know her. Maybe, we as the audience should extend that courtesy to Iwakura and get to know her. Also, as a former teenaged girl, I can say with absolute certainty, there's a good chance she breaks up with boyfriends because they expect her to put out because of her appearance. Especially since shes being set up with the gentlemanly himbo that would never push someone's boundaries like that.