The 32-year-old Keibler's friends said that despite a romantic holiday over the summer at Clooney's home in Lake Como, Italy, the couple has decided to call it quits, reports digitalspy.co.uk.
"She said George wants to be on his own again and has no intention of getting married," said a friend.
"Stacy hoped they would be together long term. It was a big breakthrough to spend time with his parents. But over the last few weeks, George has pulled away from her," added the friend.
A statement announcing the split will be released in the coming days, said their friends.
The couple started dating eachother August last year, a month after the 51-year-old actor split from his long-term girlfriend, Italian model and actress Elisabetta Canalis.
Photos: Deepika Padukone, Neha Dhupia and Soha Ali Khan at event
In pictures: 15 facts about kissing that will surprise you
Birthday special: Shahid Kapoor's best performances in Bollywood
Photos: Kim Sharma, Sagarika Ghatge, Zaheer Khan at launch in Mumbai
Photos: Kangana Ranaut looks pretty in pink