Who we are has nothing to do with our chemical makeup. We are what we’ve experienced when we weren’t alone. We are not ourselves without each other. From losing the closest friend—my ears when my mouth was busy, my mouth when my ears didn’t have the capacity to absorb anything—I gathered that I would never again be my whole self. That’s why my knees grew weak when I heard the news, why my heart is heavy as I give these gentle words a permanent home. A piece of my heart, a morsel of my brain, my thoughts, was missing and every necessary function that should happen couldn’t, because I lost a...