No one is at fault in Hemingway's narrative; it is the wartime setting that creates challenges and merely temporal settings for love that is to blame for the separation of the soldier and his nurse, Luz.
"A Very Short Story" reflects Ernest Hemingway's theme of the futility of love during wartime. Therefore, contrary to what Cassius tells Brutus in Julius Caesar, the fault is, indeed, in the stars, and not in people in wartime. That the war plays a crucial role is indicated in the story as the soldier is called back to the front, but before that, the couple wishes to marry although "there was not enough time for the banns, and neither of them had birth certificates." And so, because of circumstances, they are not able to "make it so they could not lose it." Because they cannot marry, there is no concrete commitment made before the soldier returns to the front and Luz to her job. Added to this, while Luz does write to him frequently, he does not receive any of the letters until later, after the armistice.
After the armistice, they agree that the soldier will return to America and secure a job so that they can be married. However, they quarrel and do not resolve their conflict before parting because the trains are pulling out. Luz goes to Pordenone to open a hospital where a battalion of arditi are quartered in the town, while the soldier looks for a job in the United States, all the while regretting their bitter departure.
Living in the muddy, rainy town in the winter, the major of the [Italian] battalion made love to Luz, and she had never known Italians before, and finally wrote to the States that theirs had been only a boy and girl affair.
But, the major does not love her, and Luz becomes a casualty of war, as does the soldier in Chicago's Lincoln Park during an erotic cab ride.