You're not the one
It's hurtful to be told that you're not the one that he/she wants because he/she doesn't know exactly what they want to begin with. That person you want to be with wants something/someone you're not. They're looking for a certain physical type or financial figure. Maybe they need for you to have a certain type of job or car. Its possible they need someone they can rule or run over and who can't speak up for themselves. No matter...that's not you. When someone says, "you're not the one" just smile and know that they aren't the one you want to be with.