"We've been together a long time and we just thought, 'let's solidify this,'" Nabors, 82, tells PEOPLE from Hawaii.
The former Andy Griffith Show and Gomer Pyle star and Cadwallader, 64, flew to Seattle – gay marriage is legal in Washington state – for a no-nonsense ceremony on Jan. 15, presided over by a longtime friend who is a judge.
"This was kind of dotting the 'Is' and crossing the Ts,'" Nabors says, revealing that the couple did exchange rings along with their "I dos."
"That was really weird at my age," he says, laughing. "I never thought this would happen to me. Believe me, I didn't."
Nabors has been equally astonished by the response since news broke of the nuptials.
"People have called all over and it's kind of surprised me. I appreciate the good thoughts," says Nabors, who adds that he and Cadwallader enjoy what he calls "a good life" in Hawaii. "I'm a farmer! We have a farm that's part of the National Tropical Botanical Garden on Maui and we raise macadamia nuts."
The newlyweds (the term makes Nabors chuckle) "are very happy," says Nabors. "One thing I've learned is when you find a best friend in this life you better hang on."