Stine (1967)

Pauline Pittelkow, a widow in her prime, lives in Berlin with her daughter Olga and her younger, still unmarried sister Stine. No one takes offense at the fact that the righteous woman has had an older count as a lover for years. For an evening together, the count brings a baron friend, his nephew Waldemar von Haldern and the actress Wanda. Waldemar, raised in a cold home, and the smart, solid Stine develop a deep, earnest affection for each other. The wise-beyond-life Mrs. Pittelkow does not look kindly on this ill-mannered union. She thinks that a light love affair is acceptable, but deep feelings cause pain. Despite all tradition, Waldemar wants to take Stine as his wife. The resistance of his family and Pauline drives him to take a momentous step.

Unfortunately the movie Stine is not yet available on HBO Max.