The 51-year-old actor - who was wed to Talia Balsam from 1989 to 1993 - has been dating former wrestler Stacy Keibler for over a year but his older sibling Adelia Zeidler believes her brother will always be more committed to his career than his relationships.
She told In Touch Weekly magazine: "George will probably not get married. He decided that he could have the career or he could have a family. He set goals for himself and worked hard to achieve those goals. He's very happy with his life."
While Adelia says Stacy, 33, is "very nice", she revealed George rarely talks about her.
She explained: "He'll tell me little things that are going on but mostly we just gab about inconsequential matters."
George has previously admitted his reluctance to marry has made people think he is gay, but he doesn't let the speculation upset him.
He has said: "I think it's funny, but the last thing you'll ever see me do is jump up and down, saying,
'These are lies!' That would be unfair and unkind to my good friends in the gay community.
"I'm not going to let anyone make it seem like being gay is a bad thing. My private life is private, and I'm very happy in it.
"Who does it hurt if someone thinks I'm gay? I'll be long dead and there will still be people who say I was gay. I don't give a s**t."