Tortura is a powerful word that literally translates to "torture". While it can describe physical pain, in this song, it's used to express extreme emotional agony.
Shakira sings, "Ay, amor, fue una tortura perderte" (Oh, love, it was torture losing you), making it the central theme of this passionate and dramatic breakup song. It's a perfect example of how Spanish uses strong vocabulary to convey deep feelings, making the heartbreak feel incredibly real and intense.
This song is a whole dramatic argument between two lovers, and it is brilliant. Shakira kicks things off by telling her ex to save it. She says, "guardate la poesia / Guardate la alegria pa' ti" (keep your poetry / keep your joy for yourself). She's not interested in his apologies, especially since he's crying "con los ojos secos y hablando de ella" (with dry eyes and talking about her). Ouch. She makes it clear her expectations were reasonable; she wasn't asking for perfect days, just for him not to cheat and then lie about it. The title comes from her line, "Ay, amor, fue una tortura perderte" (Oh, love, it was torture to lose you), showing how much the breakup hurt her.
Alejandro Sanz plays the guy who messed up, and he's trying every trick in the book to get her back. He admits, "Yo sé que no he sido un santo" (I know I haven't been a saint), but promises he can fix it. His excuses are almost funny. He tries the classic "No sólo de pan vive el hombre" (Man does not live by bread alone) line, implying his needs weren't being met. He even begs her, "Oye mi negra no me castigues más / Porque allá afuera sin ti no tengo paz" (Hey my girl, don't punish me anymore / Because out there without you I have no peace). But she's having none of it. Her final word on the matter is the incredibly blunt put-down, "a otro perro con ese hueso" (give that bone to another dog). She knows he won't change, comparing it to asking elm trees for pears, and she's done.