Why is it that............?

Whn you love someone you give them your heart. You love them from the bottom of yoursoul. You treat them like they are the only one on your mind and you mena it. You make sure they know that. You can lay under the stars with them and have them feel so comfortable and secure that they fall asleep on your chest for a hour. You can promise to love them forever when they ask how much to love them. And in the end, they just leave to you for someone else cause you weren't able to somehow meet what they wanted. That you weren't able to be more than just a brotherly figure. How can they say that then tell you they love you.