The Lady of Musashino 1951

In post-war Japan, Michiko, a disillusioned young woman trapped in a loveless marriage, confides in her younger cousin, Tsutomo, and the two become close, but decide not to consummate their affair. He instead becomes involved with the flirtatious Tomiko, who is also conducting an affair with Michiko's husband. When Michiko finds that her husband has abandoned her, she decides to take her fate into her own hands.