He should've been suspicious when Ron offered a cup of juice, but he'd been distracted because Ginny said yes! Listening to the guitar solo, grateful that he was wearing his school uniform sans robes–unlike the tight black dresses on the conjured band behind him–he wondered where Fred and George heard the song. Hermione probably had a hand in that.
Smiling at Ginny, whose face sparkled with laughter, Harry winked and she turned red. Singing the last part, he decided the words were wrong. If he was addicted, it was to Ginny.
"Might as well face it, you're addicted to love."
Disclaimer: I own neither Harry Potter, or the song "Addicted to Love."