How do I act?~Sirius Black

Sirius Black always saw Aubrey Jones as one of his friends, one of his best friends, if you're being generous. She was sweet. Familiar. Safe.
So what happens when Aubrey Jones steps back onto the Hogwarts Express for sixth year changed, still kind and bookish, but louder, brighter, impossible to ignore, and Sirius suddenly doesn't know how to act, or when he started looking at her like this?

"She learned how to be loud. He learned he'd been listening all along."
Sirius Black x FemOC