Sigler, 28, and Ferrara, 30, met on the set of the hit HBO series in 2008. Jamie played the love interest of Jerry's character Turtle -- and the twosome soon began dating in real life.
"They're busy with their careers, and she in particular has a couple of movies out in 2010, and others in the works for 2011, so it's just tough," a source close to the couple tells People magazine.
At the end of the last season of "Entourage," Jamie and Jerry's characters split up because of their hectic schedules -- and their real-life split is imitating art.
"It's ironic, because in the recent season finale of Entourage, Jamie tells Turtle that she has to go to New Zealand to shoot a movie, and it causes problems, so it's ironic but that's what their lives are like."