Cosette was too lost in her thoughts, not her book, to notice the scene going on near where she sat. Her thoughts of how gorgeous Sirius was, how he never really noticed her--sure they'd spoken on rare occasions. There was their first meeting a few days into their first year. The one where he bumped into her on her way back into the common room. The one where he'd wrapped his arms around her to steady her. The where she had completely embarrassed herself by stammering a soft thank you in a French accent. Odds were, he didn't remember. But she did.
It wasn't until she felt someone sit next to her that she realized that the courtyard was no longer deserted and it wasn't until she felt an arm around her and looked up in startled surprise that she realized who it was. Her mouth dropped open in a little 'O' of shock. Sitting next to her, incredibly close with his arm around her was the very person who had been in her thoughts.
She first heard him ask her a question and call her 'sugarpuss,' then she heard his whispered 'play along' she cleared her throat, trying to regain some train of thought, but it seemed to be gone. She glanced around for a second before she realized what he was doing. There was a girl glaring in their direction. He was likely using her to make the girl jealous. Typical, she thought in annoyance, but she just gave a smile and a nod. "Yes, that's right," she said softly, not even sure what she was agreeing to.