"We're dear friends, still. Kaley's not just an ex, she's a part of my life," Galecki tells CBS Watch! magazine, as excerpted by Us Weekly.
As to why he doesn't mention their past romance more often, Galecki explains: "I just don't like to speak about it. And not because I'm trying to be enigmatic; I just worry that it will conflict with people's acceptance of Leonard and Penny. I get the curiosity, but I don't want to distract from the story."
Cuoco first revealed their relationship to CBS Watch! in 2010, three years after the pair began working on The Big Bang Theory together.
"We dated for almost two years. It was such a huge part of my life and no one knew about it," Cuoco told the magazine. "This is the first time I've ever talked about it, ever. It was a wonderful relationship, but we never spoke a word about it and never went anywhere together."