why cant it be me

Your my best friends brother, I cant like you, it would go against everything friendship is, but still i feel this pit in my stomach everytime i see him. He's only a year older and we were friends before I knew her but it still feels wrong, i hide my crush for as long as i can, but you can't hide things from your best friend can you. You end up telling her and shes happy, but her brother is also in a situation with another girl. So you don't tell him and you just pretend that everything is fine, and that its not crushing your heart seeing them get closer and closer. And then all of a sudden there together and there is nothing you can do about it, so i ask, why can't it be me?