Desengaño is a powerful Spanish word for the feeling of disillusionment or bitter disappointment. It's built from the word engaño (deceit or trick), so it literally means to be 'un-deceived' or to discover a harsh truth.
In the song, DannyLux sings about "el duro desengaño" (the harsh disillusionment), expressing the painful, cold realization that a love he believed in is over. This single word perfectly captures the raw heartbreak at the core of the lyrics.
This song is a deep dive into the loneliness that follows a breakup. DannyLux feels like the quiet nights are the worst, when the silence just makes him feel more alone. He says, "Ya no estás / Y esta noche, tan callada me consume más" (You're not here anymore / And this quiet night consumes me more). The memory of his ex is so strong it's like a ghost is in the room with him, looking at him with her eyes.
He admits he loved her so much that he completely lost himself, saying "Te amaba tanto que se me olvido cómo quererme" (I loved you so much that I forgot how to love myself). He even wrote songs for her that he was never able to share. Now, he uses music to get all these feelings out because he couldn't express them before. He wonders if all this pain is necessary, this "frío en el alma" (cold in my soul), and seems to accept that he might just be alone forever. The song ends with the line "No siento nada" (I feel nothing), which is a really bleak way to finish after all that emotion.