She thinks about bringing someone else to the dance to humiliate the prince or at least make people wonder if she is no longer in love, and as she is walking, she sees a man lying down in the alley that smells terribly and goes to help him, when he gets up she notices he's actually very handsome and decides to bring him to her mansion to clean him up, dress him and give some quick lessions so he can be her date, the guy consenting and actually being polite helps with that decision.
Turns out he's mute and a werewolf, when they are in the dance, she sees the heroine and sees the prince looking at her while blushing and notices this is the moment he falls for her at first sight, later on, as for the guy she picked up on the streets, he runs away at the middle because he is being pursued, but his reactions and expressions show some guilt over abandoning Melissa and hints that despite only knowing her for two days, he likes her a bit, if for no other reason than her picking up a mute extremely dirty poor man off the streets and letting him have a good life for a short while.
I assume the guy comes back to her later seeing as he is with her in the cover, and yes, he's mute, at least, he doesn't talk at all and only speaks through gestures and face expressions, he's really damn cute at that.