Married 63 years
While a lot of actors strayed, James Cagney never once cheated on his wife in the 6+ decades they were together. Not even Merle Oberon's advances could persuade him. In his autobiography which was published in 1976, he says
"I married her in 1922, absolutely the smartest thing I ever did in the whole course of my life, and I am still crazy about this lady."