Regulus has a few older tomes with him when Andromeda bumps into him, startling him out of his thoughts and causing him to extend a hand to her arm to make sure she doesn't stumble even though he's slight enough that it shouldn't be a problem.

Shaking his head, the youngest of the Black family smiles and lofts his eyebrows. "No, it's fine. It's what happens when you're the short one, right? People miss seeing you, you get bumped into in shops..."

He's trying to act normal and it's clear - he misses Andromeda, no matter what either set of parents may say.