Extranjero means "foreigner" or "stranger". While it's a common word, its use in this song is what makes it so emotionally powerful.
In this heart-wrenching ballad, the singer fears that if his partner leaves, he'll become a stranger in his own home. The line "Seré en la casa sólo un extranjero" (I will be just a stranger in the house) creates a vivid and lonely image, perfectly capturing the feeling of losing your sense of belonging along with the person you love.
This song is a full-blown panic attack set to music. The singer's partner is about to walk out the door, and they are desperately trying to stop them. It all starts with a series of frantic questions: ¿Cómo hacer para que no te vayas? (How do I make you not leave?) and ¿Cómo hacer para que no me olvides? (How do I make you not forget me?). The singer even admits their own faults, saying, Sé que tengo tantos defectos / Queriendo hacer todo perfecto (I know I have so many flaws / Wanting to make everything perfect), and begs for a fresh start.
But it's the chorus where the desperation really hits. The singer imagines a future without their love, and it's completely empty. They'll become sólo un extranjero (just a stranger) in their own home. Even worse, Ya no habrá catorces de febrero (There will be no more February 14ths). The song paints a picture of a life that's not just lonely, but meaningless, comparing it to un tren sin estación (a train without a station). It’s a powerful plea from someone who feels they found el amor verdadero (true love) and simply can't imagine life without it.