The Liberated Woman (1972)

Sandi is a bored, restless and lonely housewife with a dull, ordinary husband who one day gets it into her mind to set out and explore the new age of free love. Her neighbor happens to be the love guru John Parker and he shows her the way, persuading her to try all the things that she's been missing out on. After experimenting with various unconventional kinds of lovemaking, including having sex with a guy that's hung like a stallion, she discovers that nothing can beat the sexual relationship she has with her husband.