Free love in America had several eras
"Free love" is associated most with the 1960's, but had been issues in the 1800's with the Oneida and other Fabian socialist communes espousing more or less equality between the sexes, the right of spouses to have other lovers if they choose, and so forth. Reactions to them included the Third Great Awakening in the mid 1800's to suppress unorthodox sects like the Mormons as well as the utopian communes.
The 1920's after WWI "free love" flourished because kids had far more mobility, experience with places outside their hometowns, and exposure to more relaxed attitudes about sexual matters in Europe during wartime, not to mention a little nihilism brought on by the horrors of combat to make one skeptical about the quaint prewar mores and social customs.
All that social disruption, feminist agitation, and so forth during the war shuffling millions of men about and employing women in war industries prompted the Prohibition effort to re-establish "decency" by banning what seemed to be the causative agent- alcohol- to the tide of "immorality".
It wasn't new, but the "flappers" managed to get everyone upset being gin-soaked party girls doing the Charleston and shagging in the backseat instead of demure lasses stringing along gentleman callers.
We're more familiar with the post-WWII period where the counterculture expanded from bohemian enclaves to a much more visible and widespread phenomenon and actually changing the social consensus toward female empowerment, the right to no-fault divorce, and de-stigmatizing premarital sex.
As to "free love" getting a longer lease on life, you have to defuse the conservative backlash by making previously outrageous increasingly ordinary to where the average individual sees it as progress worth continuing and willing to laugh anyone out of secular or religious office trying to stop it.