My song is Who You'd Be Today by Kenny Chesney. Be warned - it's a downer.
Nolan broke a promise to his sister, and even though neither of them knew the repercussions that would have, she died because of it. So he struggles with his guilt, knowing if he'd only kept his word, it would never have happened.
She wanted so much, dreamed of so many things. Gone in a heartbeat. So he wonders.