Desvelándome comes from the verb desvelar, meaning "to keep awake." The -me ending makes it reflexive, so it translates to "keeping myself awake" or more commonly, "losing sleep."
In the song, Ivan Cornejo sings, "Yo desvelándome pa' sólo ayudarte" (Me losing sleep just to help you). This single word powerfully illustrates the personal sacrifice and one-sided effort in the relationship he's mourning. It paints a vivid, relatable picture of staying up all night for someone who ultimately broke his heart.
Ivan Cornejo does not sugarcoat a breakup in "Corazón Frío" (Cold Heart). He starts off completely frozen over, singing, "Mi corazón, ya está frío / Me lo quebraste ahora no creo en amor" ("My heart is already cold / You broke it, now I don't believe in love"). Instead of talking it out, he grabs his instrument because "Cantando es mi única forma de expresar" ("Singing is my only way to express"). It turns out losing sleep to support an ungrateful ex really takes a toll. He bluntly complains that his ex damaged his physical well-being: "Y mi salud, me la dañaste / Yo desvelándome pa' sólo ayudarte" ("And my health, you harmed it / Me staying up late just to help you").
There is great everyday slang here for language learners. Cornejo sings that his wasted hours are like "feria gastada" ("spent change" or "spent cash"), using the Mexican slang "feria" for money to show his time was treated like loose pocket change. All those late-night calls where his ex claimed to miss him? Completely fake ("eran tus falsas palabras" ["they were your false words"]). By the time he reaches the chorus, he reaches a blunt, harsh verdict: "Ahora tú eres nada" ("Now you are nothing"). He accepts that "sentimientos cambian" ("feelings change"), turning bitter exhaustion into his signature sad sierreño sound.