When Rio and Ray married in 2008, the Bay Area women omitted two words from their wedding vows: fidelity and monogamy. “I take it as a gift that someone will be that open and honest and sharing with me,” said Rio, using the word “open” to describe their marriage. Love brought the middle-age couple together — they wed during California’s brief legal window for same-sex marriage. But they knew from the beginning that their bond would be forged on their own terms, including what they call “play” with other women. As the trial phase of the constitutional battle to overturn...