Billie Jean King Announces Affair with Marilyn Barnett at Press Conference (April 1, 1981)

Billie Jean and Larry King were engaged in fall of 1964 and married in Long Beach, California, on September 17, 1965.[10][185] Billie Jean credited Larry with introducing her to feminism and for pushing her to pursue tennis as a career.[20] Billie Jean later said she "was totally in love with Larry" when they married.[125]

By 1968, King realized that she was attracted to women.[186] In 1971, she began an affair with her secretary, Marilyn Barnett (born Marilyn Kathryn McRae on January 28, 1948). Barnett had been living rent-free in the Kings' Malibu house. In 1979, the Kings asked Barnett to leave their house, but she did not want to. Refusing to leave the house, Barnett threatened to leak records and receipts that she had kept over the years. These receipts included letters from Billie Jean to Marilyn, credit card receipts, and paid bills. After a suicide attempt where she jumped off the balcony of the house leaving her a paraplegic, Barnett sued the Kings in a May 1981 palimony lawsuit for half their income and the Malibu house where she had been staying. Billie Jean acknowledged the relationship between her and Marilyn shortly afterward, making Billie Jean the first prominent female professional athlete to come out.[187] Feeling she could not admit to the extent of the relationship, Billie Jean publicly called it a fling and a mistake. The lawsuit caused Billie Jean to lose an estimated $2 million in endorsements and forced her to prolong her tennis career to pay attorneys.[148] In December 1981, a court order stipulated that Barnett leave the house and that her threats to publish private correspondence between her and King in exchange for money came close to extortion. Barnett's palimony suit was thrown out of court in November 1982.[188] But in a bizarre twist of fate, a few months later in March 1983, the house that had been contested was destroyed during a series of freak storms that lashed the southern California coastline.[189]

Also in 1971, King had an abortion that was made public in a Ms. magazine article.[186] Larry had revealed Billie Jean's abortion without consulting her.[186]

Concerning the personal cost of concealing her sexuality for so many years, Billie Jean said:

I wanted to tell the truth but my parents were homophobic and I was in the closet. As well as that, I had people tell me that if I talked about what I was going through, it would be the end of the women's tour. I couldn't get a closet deep enough. One of my big goals was always to be honest with my parents and I couldn't be for a long time. I tried to bring up the subject but felt I couldn't. My mother would say, "We're not talking about things like that", and I was pretty easily stopped because I was reluctant anyway. I ended up with an eating disorder that came from trying to numb myself from my feelings. I needed to surrender far sooner than I did. At the age of 51, I was finally able to talk about it properly with my parents and no longer did I have to measure my words with them. That was a turning point for me as it meant I didn't have regrets anymore.[125]
Billie Jean and Larry remained married through the palimony suit fallout.[20] Their marriage ended in 1987 after Billie Jean fell in love with her doubles partner, Ilana Kloss.[20] Billie Jean and Larry nevertheless remained close, and she is the godmother of Larry's son from his subsequent marriage.[20] On October 18, 2018, King and Kloss were married by former New York City Mayor David Dinkins in a secret ceremony.[190]

King and her wife Kloss have residences in New York City and Chicago.[191][192]

King is a vegetarian.[193]

It was announced in March 2021 that King will be an advisor to First Women's Bank in Chicago.[194]