I'm pretty sure the extra is a girl, seeing as during the conversation they said MC is known for only paying attention to the guys, if extra was a guy I don't think they'll say that. That and because of the long hair, seeing as the novel in the manwha takes place in modern Korea, it's unlikely guys would have long hair. I mean I'm down for a yuri route, but I'm also down for a route where it's the MC slowly making friends rather than romance.