Nublando comes from the verb nublar, meaning 'to cloud over' or 'to darken'. It's a descriptive word that paints a vivid picture of something becoming obscured or less clear.
In the song, the lyric "Se va nublando cada día mas el cielo de mi esperanza" (The sky of my hope is clouding over more each day) uses nublando metaphorically. It beautifully conveys the feeling of hope diminishing and becoming obscured by sadness, making it a powerful and evocative choice.
This song is pure heartbreak, but the kind that feels slow and heavy, not loud and dramatic. The singer is stuck on a love that ended a long time ago, while the other person has already moved on and “has shelter now” somewhere else: “y saber que ahora ya tienes abrigo” [and knowing that now you already have shelter]. Because he kept thinking she would come back, his hope is collapsing: “se va muriendo mi alma” [my soul is slowly dying] and “se va nublando cada día más el cielo de mi esperanza” [every day the sky of my hope gets more cloudy]. He feels empty, watched, and uncomfortable in his own life: “porque tengo temor a las miradas” [because I’m afraid of people’s looks], like everyone can see how broken he is.
The worst part for him is that the love itself will not leave: “es tu amor el que no me deja vivir” [it’s your love that won’t let me live]. He can’t give it up “del que no puedo desistir” [which I can’t give up], because it stayed deep inside “como una luz que nunca se apagó” [like a light that never went out] and “como una noche eterna que nunca amaneció” [like an eternal night that never saw dawn]. Forgetting feels impossible: “¿cómo es posible olvidar la única vez que supe amar?” [how is it possible to forget the only time I knew how to love?]. What hurts the most is the contrast: for him it was “lo más bello que jamás sentí” [the most beautiful thing I ever felt], but now it only hurts “y tú ni te acuerdas de mí” [and you don’t even remember me]. It’s a song for when you still feel everything, and the other person feels nothing.