Ron had excused himself from Hermione, and had passed by the drinks table. He'd grabbed a cup of punch and downed it on his way to the loo. He was on his way back, feeling more than eager to go and find Hermione again. Still thirsty, he grabbed another cup of punch and stood for a moment, not far from the refreshment table as he watch the crowd. He didn't see Hermione where he'd left her, and thought she might be dancing with someone else. The idea of it made his stomach tighten a bit, but he decided he wouldn't let himself be jealous; he'd left her on her own, so she could dance with a few other blokes, he guessed. Heck, maybe he'd get up his courage and try to dance with a different girl.
He liked the idea of being brave, and he rocked on his heels, enjoying the music, and reached for a third cup of punch. As soon as he spied her, he'd bring her some as well.