The star of the new crime drama A Most Violent Year tells PEOPLE, "I'm not quite sure of what I want in my life"
Credit: Dimitrios Kambouris/Getty

Her boyfriend is a real-life Italian count, but Jessica Chastain isn’t looking to take on the role of countess anytime soon.

“I’m not quite sure of what I want in my life, and who knows if marriage is a part of it,” says the actress, 37, who has been dating Italian fashion executive Gian Luca Passi de Preposulo since 2012. “So to me, marriage is not an important thing.”

When it comes to their romance, “everything is fantastic,” she tells PEOPLE in this week’s issue, lauding her boyfriend’s “passion for the arts.”

Onscreen, the star – who appeared in four movies last year, including the sci-fi blockbuster Interstellar – is earning critical raves as a steely wife in the crime drama A Most Violent Year, opening in wide release this month.

In one memorable scene, she defies an investigator with the toss of a cigarette.

“That was a Chastain invention,” she says. “I had no idea people would be coming up to me and flicking a cigarette and quoting my line, ‘This was very disrespectful.’ It’s very cool.”

See the scene below:

For more on Jessica Chastain, pick up this week’s issue of PEOPLE, on newsstands Friday

Reporting by MARY GREEN