Pansy Parkinson - She'd probably sneer at him, but would necessarily go out of her way to pick on him or anything--she's a business woman now, so has to keep that in mind.
Harry Potter - He'd be friendly enough, but they probably wouldn't know each other well right now. Always up for any interactions!
Lisa Turpin - She's a Muggleborn, and owns a bookshop in Monument Alley. She spent the last 7 years in San Francisco and only just moved back. She'd be friendly!
Ben Stebbins - He's one of the bartenders at Finnigan's, so he'd know Romeo from there. He thinks he's adorable, and probably has a big brother attitude towards him.
Terry Boot - He's a Quidditch player, and also a regular at Yoga. He'd definitely join a GSA, and would be friendly enough if not outgoing.