Be an adult with some class and self-control. Call him up, explain what you heard, and cancel the date. Don't do it in a fit of anger, but instead show him how little he affected you. Your dignity will remain intact, he'll realize he screwed up and did something disrespectful, and it will end gracefully with maybe an apology on his end.
Or do the vengeful thing. Make him burn his time and money and then slam it in his face. Become a "bitch" to him and all his friends and enjoy a new enemy in your life. See how that goes for you.