i am not that guy
The guy your girl runs to when you're not around, like you're not even worth the effort of being her main guy.
"He's not that guy! He's the guy who only shows up when I'm not looking!", Your girl, after she texts your ex.
"He's not that guy! He's the guy who thinks he's better than you!", Your girl, after she spends all her money on him.
"He's not that guy! He's the guy who doesn't even know what a real man is!", Your girl, after she dumps you for the third time this month.