warm and subtle charming but why did it get a R rating?

In 1967 in America, a film in which a woman had an abortion, as is shown here, would have been enough to earn the film an R rating. Beyond that, in 1967 America, a film showing a younger woman having an affair with an older man, then going to a younger man, and then coming back to the older man who was accepting of her would have been considered risque enough for an R rating. Remember, this film is 40 years old, and a lot has changed in those 40 years.