This is a breakup song from someone who can't stop overthinking. Marc Segui starts already lost: "Hace ya rato que buscándote, me pierdo" (I've been losing myself looking for you for a while now). He even gives up the argument, "Quédate con la razón y ya está" (keep being right and that's that), because who was right no longer matters.
The chorus plays on the verb "subir" (to go up, to lift). "Ya nada me sube" (nothing lifts me anymore) is the low point, and "Hasta por las nubes" (all the way up in the clouds) is where he used to be. The images are small and sharp: they were "hanging by a thread" that snapped from pulling too hard, and he broke "como la punta de un lápiz" (like the tip of a pencil). By the bridge, nights have no end and days have no colour. Notice "to'" and "pa' mí", the clipped forms of "todo" and "para mí" you will hear all over Spanish pop.