The Lovers (1958)

The plot of this film revolves around a married woman's unhappiness with her marriage and her subsequent affairs with other men.One of these affairs becomes sexual within the plot of the film, and we see the couple kiss passionately while laying on a boat on a lake. There is a subsequent scene in which the two make love. While the sex is not shown explicitly, we do see breast nudity and from the erotic nature of the scene it is clear that both people are enjoying their lovemaking.