Back Street (1932)

In turn-of-the-century Cincinnati, vibrant shop girl Ray Smith (Margaret Sullavan) falls in love with banker Walter Saxel (Charles Boyer), who is engaged to a socially prominent woman. Inadvertently prevented from running away with Walter, Ray remains single but reunites with him five years later. Despite Walter being married and having a son, Ray becomes his mistress, and over the years suffers social ostracism and long stretches of solitude while waiting for their brief interludes together.