Culpable means 'guilty' or 'at fault'. It's a powerful word that reveals the singer's deep regret over a past mistake.
In the song, the narrator admits, "Y aunque yo sea culpable de aquella triste separación" (And even though I may be guilty of that sad separation). This confession adds a layer of sorrow and personal responsibility, making her plea for reconciliation much more emotional and compelling.
This is a classic song about regret and heartbreak. The singer is walking alone, completely lost since a painful separation. She feels so abandoned that she says, "Ni el cielo me contesta / Cuando pregunto por ti, mi bien" (Not even the sky answers me / When I ask for you, my love). The breakup seems to have been caused by "sombras de duda y celos" (shadows of doubt and jealousy), and she even admits she might be the one at fault for the "triste separación" (sad separation).
The whole song is built around a powerful central image. In her dreams, she and her lover are together, walking towards a "cielo azul" (blue sky), a symbol of happiness. But her reality is much harsher: "Pero cuando despierto / Mi cielo es rojo, me faltas tú" (But when I wake up / My sky is red, I'm missing you). The red sky represents her pain and loneliness. She begs her former lover to forget the past and let her find them again, pleading for them to come back.