This is a breakup song from someone who flat out refuses to pretend he is fine. The hook says it plainly: "No hay manera, ni aunque quiera, de olvidar dónde fui feliz" (There's no way, even if I wanted to, to forget where I was happy).
He piles up comparisons that are half heartbreaking, half funny. Asking him to forget her is "como decirle a un niño que mamá no está aquí" (like telling a child that mom isn't here). He waits for her "como Zidane el centro de Roberto" (like Zidane waiting for Roberto's cross), a football image of a striker hanging on for the perfect pass, and "como mi abuela verme en otro concierto" (like my grandma waiting to see me at another concert). The football keeps coming back: "Cómo duele que pitaras el fin del partido" (How it hurts that you blew the final whistle). Pitar is what a referee does with the whistle, so she is the one who ended the game.
He also swears, so heads up: "En qué coño hicimos mal" (What the hell did we do wrong) uses coño, a very common but vulgar Spanish intensifier. My favourite line is the quietest one: "No te mando los mensajes, pero los escribo" (I don't send you the messages, but I write them). Anyone who has typed and deleted a text at 2am knows exactly that feeling. And when she is gone, "está lloviendo y soy de papel" (it's raining and I'm made of paper).