McMillan married Jamaican native Jonathan Plummer in 1998. When they married, McMillan was in her mid 40s, Plummer, his early 20s; he was the inspiration for the love interest of the main character in the book How Stella Got Her Groove Back. Her life did not follow the movie when in December 2004, Plummer told McMillan that he was gay; in March 2005, she filed for divorce. The divorce was settled for an undisclosed amount. In March 2007, McMillan sued Plummer and his lawyer for $40 million citing an intentional strategy to embarrass and humiliate her during the divorce proceedings; McMillan eventually won a judgement intentional infliction of emotional distress but had also withdrew the suit before the case went to trial, and Plummer was never ordered to pay the intended amount.

On September 27, 2010, the two sat together with Oprah Winfrey to discuss their post-divorce relationship and partial reconciliation; both acknowledged that he fulfilled the role of boyfriend and husband before his coming-out, although McMillan stated that "he's not my BFF".