I think I'd be upset if that happend to me, (if you reversed the genders, because Im a girl)
I still havent gotten over something that happened in my first year, 2 years ago
the past is something that is exceptionally tricky to let go of. Many of us find it hard to move on, and the main reason for that is that we havent found something better. If he loved this girl, but hasnt loved anyone since, it will be hard to forget her. If he had his ego damaged, but no one has restored it since by fancying him madly, then that may be the issue. If he now feels rejected, and hasnt met someone good and kind to show him not everyone will reject him, the same applies. To get over the past, we must have some hope for the future, some evidence that it will be good, better than the past, even. Give your friend hope with words of encouragement, help him find someone who will treat him much better than this girl did, and remind him that he has your friendship - someone to listen whenever he's down, even if you've heard it a thousand times before. Show him you'll always, always be ready to listen again, if thats what he needs.