Delirio refers to a state of delirium, intense excitement, or something that feels wildly irrational. In the song, "qué delirio sin ti" means “what madness without you,” capturing the overwhelming, almost dreamlike feeling of life in the street without the other person.
Fito Páez sets this song in a real place: Parque Patricios, a neighbourhood of Buenos Aires, where "Existe un refugio para la gente que no tiene a nadie" (there is a shelter for people who have no one). He tells us he went there to sing one night with a piano, and saw a sign that said "la calle no es un buen lugar / Para vivir, mucho menos para morir" (the street is not a good place to live, much less to die). The verses stay close to the people who live there: brothers who are "buscando un lugar" (looking for a place), who want a roof where they can pray to God and get some sun, and whose hunger "vive en el estómago" (lives in the stomach).
Then the chorus opens up into a dream: "Quiero vivir en la ciudad liberada" (I want to live in the liberated city). It is a city "Donde el amor explote en todas las plazas" (where love explodes in every square) and "Donde a los pibes no les metan mas balas" (where they don't put any more bullets into the kids). Páez mixes anger, like the line about fighting the Nazis and fascists, with pure appetite for life: loving "el sol, el cielo, el vino y la primavera" (the sun, the sky, the wine and the spring). For a learner, the chorus is a gift: vivir, amar and morir come back again and again, so you will know these verbs by heart.