In papers filed in Contra Costa County Superior Court, McMillan, 53, says she decided to end her 6½-year marriage to Jonathan Plummer, 30, after learning he is gay.
The revelation led her to conclude Plummer married only to get his U.S. citizenship, she said. McMillan met Plummer at a Jamaican resort a decade ago.
"It was devastating to discover that a relationship I had publicized to the world as life-affirming and built on mutual love was actually based on deceit," she said in court papers. "I was humiliated."
In response, Plummer maintained McMillan treated him with "homophobic" scorn bordering on harassment since he came out to her as gay just before Christmas.
McMillan is seeking to have the marriage annulled; Plummer has asked the court to set aside a prenuptial agreement that would prevent him from getting spousal support.
McMillan filed for divorce in January, but news of the split didn't surface until this week, when it was first reported in a San Francisco Chronicle gossip column. Earlier this month, a judge ordered McMillan to pay Plummer $2,000 a month in spousal support and $25,000 in attorney's fees until the case comes back to court in October.
McMillan's latest novel, "The Interruption of Everything," is scheduled to hit store shelves next month. It plots the mid-life adventures of a married mother of three who is questioning her comfortable suburban life.
McMillan said she did not plan to let a divorce "detract from the many blessings in her life," according to a statement released through her publicist.
Plummer's attorney could not immediately be reached for comment.