Leifer believes a growing number of middle-aged women are listening to what she calls the "Sapphic siren call," or as Elaine Benes, the "Seinfeld" character based on Leifer, would say, "joining the other team."
"Life threw me a surprise party," she told ABCNews.com. "Not that there's anything wrong with that. I was looking for something fun and chic. I didn't think it would redefine me as a person.
"My feelings for men were very real and powerful, but I fell in love with my partner," she said. "It's been the best relationship of my life."
In 2004, "Sex and the City" star Cynthia Nixon left her boyfriend of 15 years and their two children and began seeing a female public school advocate, whom she'd met while working on a campaign to reduce class sizes in New York City.
"I have been with men all my life and had never met a woman I had fallen in love with before," Nixon told the London Daily Mirror. "But when I did, it didn't seem so strange. It didn't change who I am. I'm just a woman who fell in love with a woman."
Novelist and social critic Susan Sontag remained in the closet until her longtime lover, photographer Annie Leibovitz, outed her posthumously. Sontag, who had been married and had a son, died of cancer in 2004 at the age of 71. She had been in a romantic relationship with Leibovitz, now 59, since 1989.
ABC News' Susan James contributed to this story.