A Letter to Three Wives (1949) on Netflix

In a small town, three couples are close friends: the upper class Brad Bishop went to the war and returned married with the insecure country girl and Navy military Deborah Bishop; the university professor George Phipps is married with the writer of silly screenplays of radio soap operas Rita Phipps, who makes more money than him and financially supports their home; and the wealthy tradesman Porter Hollingsway is married with the smart Lora Mae Hollingsway. In common, further to their friendship, the women hate and the men love the elegant and high-class Addie Ross. While going to a picnic in riverboat with the local students, the three wives receive a letter of their "friend" Addie Ross informing that she is running off with one of their husbands. Along the day, each woman recalls events that might have put her marriage in danger, while anxiously waiting for the end of the day.