My Grandfather told me that back during WWII things got so crazy you would wake up in the morning and have to introduce yourself to the woman beside you in bed!
There were times when such things were more open, and times when such things were kept more behind closed doors; but I don’t imagine there was EVER a time when such things did not go on.
But the ‘end of the world’ feeling of WWII - and the numerous young men sent off to war - and the ‘professional’ women complaining about the ‘amateurs’ “giving it away!” - and the recent advent of the automobile and the sexual license it allowed - all made that time “rather interesting” to hear my Grandfather tell it.
There was an old Dagwood comic strip where the son walks in all goo-goo eyed and Dagwood asks him what's going on. The kid retorts "Your generation wouldn't understand anything about love" and prances off. Dagwood turns to Blondie and says "And I suppose he thinks we're just good friends."
My grandmother who was a “flapper” said the roaring ‘20s made the ‘60s look like kindergarten.
My great uncle told me the same thing. Lot's of sex at the Canteen and USO shows. All those short month long romances you heard about back then the couple was married was because they HAD too because the woman was preggo.
People had the same amount of premarital sex in the 1940's and 1950's as today but it was just kept quiet.