Se me vuelve un ocho is a fantastic Spanish idiom that literally translates to "it turns into an eight for me". The phrase is used to say that something has become a complete mess or is all tangled up, like the looping shape of the number 8.
In the song, Shakira sings "la vida se me vuelve un ocho" (my life becomes a mess) to express the utter chaos and confusion she feels without her love. It's a creative and visual way to describe how her world falls apart when they're not there.
Have you ever lost something and looked for it everywhere, even in the most ridiculous places? That's the feeling at the center of Shakira's early hit, "Dónde Estás Corazón." The singer is desperately searching for her lost love, asking over and over, "¿Dónde estás, corazón?" [Where are you, my heart?]. She feels like her whole world is falling apart without them, saying her life "se me vuelve un ocho si no estás aquí" [becomes a figure eight if you're not here], a great Colombian expression for when everything gets tangled and complicated.
What makes this song so fun is the wild list of places she looks for this person. It starts big, between "el suelo y el cielo" [the ground and the sky], but then gets hilariously specific. She checks the closet, the alphabet, under the car, and even "en cuadros de Botero" [in paintings by Botero], a famous artist from her home country of Colombia. The search gets more and more personal, as she looks in her coin purse and finally admits, "Te busqué hasta en mis canciones" [I even looked for you in my songs]. It's a dramatic and slightly obsessive declaration of love, where she's convinced this person has to come back because there's simply no one else for her on the entire planet.