No, but there sounds like there is a lot more to the story. Maybe she wanted something and he didn't?
Unless she is one of those strange possessive people that never get over any of their flings.
But I might take the time to find out whether she still likes him, and whether she still talks to him etc.
Personally, in the same situation, I would still take the girl to the semi formal. I would figure he had his chance, now its my turn.