There have been rumors about his sexuality swirling for ages, but nothing has been proven. He seems like the kind of man who, if he were gay, he wouldn't care who knew. But there is the thought that he might have not enjoyed the same power as a leading man if he were out all along.
He gets more press for dating much younger women, and the relationships inevitably end, and he goes back to his Italian villa to entertain friends until the next movie is ready to go.
I think of him as this generation's Cary Grant. Grant's sexuality was an open secret in the industry, but was never made public until after his death. (Some of his loved ones are even now disputing that he ever had gay relationships.) If Clooney wants to be in the closet until he's too old to play leading men, I'm okay with that. His body of work is pretty great, and if that was the price he had to pay, I understand. He's always been a supporter of gay causes and has never been accused of being homophobic. Personally I think he's straight. If there's some plane crash someday, we'll find out for sure as people come out of the woodwork.