"Dear Serena: My world is falling apart, and you’re the only one who would understand. My father left my mother for a 31-year-old model. A male model. I feel like screaming because I don’t have anyone to talk to. You’re gone, my dad’s gone, Nate’s acting weird… Where are you? Why don’t you call? Why did you leave without saying goodbye? You’re supposed to be my best friend. I miss you so much. Love, Blair.