The Cranes Are Flying (1960) on Netflix

As the clouds of war spread over Russia during Germany's surprise invasion in 1941, the fervent young lovers, the sensitive Veronika and the stalwart Boris, are parted when the patriotic lad secretly volunteers for the war effort. During the following hard years, Veronika who serves her country as a wartime-nurse will lose communication with Boris, moreover, when a devastating air raid destroys her house and Boris' father takes her in to live with the family, unexpectedly, things will take a turn for the worse. Before long, the worried fiancée will find herself dealing not only with the dark thoughts of Boris' potential loss but also with the burden of an unwelcome decision. Once, the star-crossed lovers swore eternal devotion under a flock of flying cranes, still, a war is always cruel and eternally disastrous.