He shows clear attraction to her.
He is worried about Tom, but if he really thought Star was in danger you'd think he'd have gone after her right away or put up more of a fight about her going. Instead, he sits at home sulking like a kid who couldn't find a date to the prom, until a mysterious voice tells him the Blood Moon is the "moon of lovers."
When he finds Star, he doesn't just watch out for her from the crowd or take her aside to check on her or bring her home, he grabs her hand, pulls her close and takes the lead in a full-on waltz.
When they get home, she rebukes him for not trusting her to take care of herself, and tells him she doesn't want him to be her hero, just her "friend." Marco doesn't look remorseful for upsetting her, he looks heartbroken for being rejected. She didn't mean it that way, but that's how he took it.