Astronauti means astronauts in Italian. It is a striking and unique word that immediately sets a cosmic, introspective tone, evoking isolation and distance even between two people who are physically close.
Gianmaria sings "Due astronauti nello spazio vivevano al contrario" (Two astronauts in space lived backwards), using the word to describe two people who are together yet emotionally isolated, like astronauts floating alone in space.
"Astronauti" uses space as a metaphor for a relationship that has drifted apart. The narrator describes floating alone, short of air, in a room stripped of anything alive - no rain, no warmth, nothing left.
He admits that choosing his career over the relationship left him isolated long before the breakup, and that he might have been better off without her.
The chorus imagines two astronauts locked in a dying capsule, each having to choose who survives and who is left behind. It's a dramatic way of saying that staying together the way they are means one of them has to give something up.
The final verses look back at the relationship itself: two people forced together, unsure if any of it was real, who never really let anyone else in. The song ends on the same impossible choice repeated - choose him, choose her - with no easy answer.