The Thief (1997) on Netflix

Plot summary

Katya's son Sanya was born in 1946, after his father died, and she has raised the boy alone through the lean years that followed the war. Sanya never knew his father, though he often pictures him. In 1952, the two of them meet Tolyan on a train, a charming officer who pays court to Katya. She falls in love, and the three begin living together, Tolyan calling himself her husband and taking on the part of father to the boy. Sanya resists at first, then grows fond of him and finds protection and comfort in his company. The people around them take to Tolyan for his generosity, and his lessons to the boy are about fighting back and winning at any cost.