Nido literally means "nest". While it's a common word, its use in this song is particularly evocative and poetic.
Here, the singer uses nido metaphorically to represent a safe, intimate home or relationship that fear has driven her lover away from. It paints a vivid picture of lost comfort and security, making it a memorable and emotionally resonant word.
This song is pure drama! Natalia Oreiro's partner has just walked out on her, slamming the door without a single word: "Te marchaste sin palabras, cerrando la puerta" (You left without words, closing the door). The worst part is the timing. It happened just as she was asking for more from the relationship. She thinks he left out of fear, and now she's left with a "corazón herido" (wounded heart).
The chorus is a massive, desperate plea where she repeats, "Me muero de amor si no estás" (I'm dying of love if you're not here). Later, she finds a letter he left, but his explanation makes no sense to her. He claims he needed space, a "falta de aire" (lack of air), but she completely disagrees, singing, "Si siempre te dejé ser libre, sin una condición" (When I always let you be free, without any conditions). She's left totally confused and hoping it's all a bad dream she'll wake up from.