An ex girlfriend is a female who you used to be romantically involved with, and then the relationship broke apart. This can happen for many different reasons. Sometimes an ex girlfriend is still considered a friend, but far too often the relationship ended on bad terms and this female now views you as an enemy or someone that they want to forget.
I wish I didn't fall so deep in love with you and now there ain't no way we can be friends.
I DON'T have EX's! I have Y's. Like 'Y the hell did I date you?!
Be the girl his ex girlfriend will hate, his mom will love, and that he will never forget.