The Downton Abbey star, who has been famously candid about her love life – which has included a handful of affairs – says that the only way to ensure marital success is to take an open approach to monogamy.
Detailing her relationship with film producer Steve Parker, MacLaine tells PEOPLE and Entertainment Weekly Editorial Director Jess Cagle during a Sirius XM town hall that she and her husband of 28 years were friends more than lovers.
Cindy Ord / Getty
"I guess you would say 'practiced an open marriage' in 1954, which was another lifetime," she says. "No one understood it, we did. He lived in Japan basically, I lived in America working, and this and that."
She continued, "We'd meet up, always great friends, traveled sometimes together."
The couple split up in 1982, but not before welcoming one daughter, actress Sachi Parker. Parker was mostly raised by her father, a childhood she later detailed in a 2013 tell-all book her mother called "virtually all fiction."
Watch more of The Jess Cagle Interview with Shirley MacLaine on PEOPLE.com all day Thursday
Regardless, MacLaine stands by the relationship with the man she once told The Guardian was the "love of my life."
"I think that's the basis for a long-lasting marriage, if you really want to do such a thing," she shares. "I would say better to stay friends and we don't have enough time to talk about the sexuality of all. I was very open about all of that and so was he."
Gene Lester / Getty
These days, MacLaine's romantic life is a little less intense, but not without drama.
"I'm having a relationship now, that is teaching me about possessiveness with intimacy and it's with my three dogs," she deadpans. "I adore my dogs. And I've had to get a dog nanny/food lady for the dogs because I've been working so much."
The nanny has weaseled her way into the pups' hearts though, and instead of turning to MacLaine for comfort, they've become attached to the new caregiver.
"It is tough, I'm not kidding you," she says. "Totally indiscreet … I'm really learning what people will do for food."
Shirley MacLaine's latest book, Above the Line, is available now. Her Town Hall on Sirius XM, hosted by PEOPLE and Entertainment Weekly Editorial Director Jess Cagle, will be broadcast March 24 at 2 p.m. ET on EW Radio.