With one swift movement Draco managed to destroy his entire life.
It had been apparent from the beginning that he was only there to piss off his father. Mission totally accomplished. But he had been happy for a while and that was obviously shot to hell now.
Draco didn't initiate the hug. Charlie was leaving for Christmas and it had just happened. The kiss... could have easily been explained as a spoiled rich kid thing. Eccentric behavior was normal, right? Until Draco had opened his mouth and used tongue.
After that, he was pretty certain it was all his fault.