Although the 1972 book, Open Marriage, is often considered the source for the term open marriage, George and Nena O'Neill only briefly mentioned extramarital sex in marriage.
Mo'Nique about open marriage: "Open means, you know what, let me tell you my every secret, my fantasies, my thoughts, so that way, there are no surprises ... I have not had sex outside of my marriage with Sidney. Could I have sex outside of my marriage with Sidney? Yes. Could Sid have sex outside of his marriage with me? Yes. That's not a deal-breaker."
Source: Lauren Sher. "Mo'Nique on Sex Outside Marriage: 'That's Not a Deal-Breaker.'" ABCNews.go.com. 3/04/2010.
Shirley MacLaine on her open marriage: "I was married for 30 years, but he lived in Japan. I lived with many other men ... Men always wanted to get married, in my experience. So I stayed married to Steve so that I wouldn't marry them."
Source: Sarah Hampson. "At 74, Shirley MacLaine ..." Globe and Mail. 9/14/2008.
Source: Will Smith and Jada Pinkett Marriage Profile