While we've got 'em up on the monitor

Rico says that, much to his surprise, he ended up pleased that they moved Big Bang Theory to Thursday nights, even though it broke up the bloc of splendid comedies (How I Met Your Mother, Rules of Engagement, Two and a Half Men) on Monday night, because it's on at eight now, instead of 9.30, so he can go to bed earlier on Mondays.
Turns out that the on-screen romance between Kaley Cuoco and Johnny Galecki was only mirroring reality, according to an article by Matt Mitovich on Fancast:

No bazinga here – ‘Big Bang Theory‘ costars Kaley Cuoco and Johnny Galecki really did carry on a real-life romance during the show’s early run, and worked hard to keep it under wraps.
“We dated for almost two years,” Cuoco tells CBS Watch. “It was such a huge part of my life and no one knew about it.” Speaking publicly for the first time about the romance, Cuoco says the relationship was “wonderful”, despite the way she and Galecki were forced to keep it secret. “We never spoke a word about it and never went anywhere together,” she recalls. “We were so protective of ourselves and the show and didn’t want anything to ruin that. But that also made it sad, too. That’s not the kind of relationship I want. I don’t want to be hiding.” Cuoco says that she wanted to go public as a couple, but “certain people didn’t want to do it that way, which I understand.”
The Cuoco-Galecki romance was not the For Your Eyes Only, government-caliber top secret that some are painting it to be in the wake of Cuoco’s admission. No, TV Guide reported on the relationship as it was happening, in the fall of 2008. Cuoco, though, would not confirm the news.
“Everyone was always asking, and we deny-deny-denied,” she says now. “I’m like, ‘Why am I denying this person that I love?’ It took a little bit of a toll on me, and I think it did for him, too.”
When Cuoco and Galecki ultimately called it quits, they took measures to keep their emotions in check and CBS’ then-blossoming comedy on track. “We decided we’re not going to screw it up, and we’re not going to screw it up for everyone else and make things weird,” she says. “There was so much at stake, and we both knew that.”