The Big Bang Theory - Johnny Galecki, Kaley Cuoco The Big Bang Theory - Johnny Galecki, Kaley Cuoco

After two seasons of longing stares, unrequited sexual tension and many close calls, Big Bang Theory fans rejoiced earlier this season when Leonard (Johnny Galecki) and Penny (Kaley Cuoco) finally got together. Unfortunately, trouble in paradise is ahead for the beauty and the geek.

"There will be some turmoil with Penny and Leonard," Galecki says of the show, airing Monday at 9:30/8:30c on CBS. "They're still very far from being able to truly click. They're too different and they both have so much to learn. They both have a long way before they meet on equal territory."

The relationship has been a challenging new experience for both; since it's both Penny's first serious relationship on the show and one of the first relationships altogether for Leonard. "She's starting to deeply realize that maybe he is the one, but not right now. She has her own baggage," Cuoco says. "She's a little more not so sure what she wants, and I think the minute she loses Leonard, she's going to regret it for a long time."

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It remains to be seen if or when Penny and Leonard will re-enter the dating scene, but Galecki thinks the possibility is an interesting one. "[Penny's] really fed his confidence in a way that he hasn't had before. I think that he'll take that into the next relationship," he says. "It seems like, fortunately, they'll have some time exploring that."

Now that Penny and Leonard's relationship has an expiration date, Cuoco is thankful that, despite fans' enthusiasm for the pairing, the relationship has not become the main attraction. "I like that it's not the main focal point of the show, so when it does end, its not going to be shocking," she says. "It has to end at some point."

A main struggle going forward will be keeping the group together despite the open wounds from the relationship. "The five of them can't live without each other," Kunal Nayyar (Raj) says of the series' dynamic. "These guys can't live without Penny either."

Sheldon (Jim Parsons) may be hardest hit by the split. "It might be much harder on Sheldon than we all think because he's finally come to grips with things the way they are," Cuoco says. "I don't even think it's because he's sad for us, it's about him ... how is this going to affect Sheldon? He's not going to be able to cope."

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Although he's Leonard's roommate and best friend, Sheldon's growing bond with Penny will put him squarely in the middle of the two in future episodes. "I do think it's because she's very mothering to him. She's probably the only person that's that nice to him," Cuoco says. "Even the guys can't stand him at moments. She really has a soft spot for him and the audience loves that."

So does this mean Penny may find romance with Sheldon once she splits from Leonard? Cuoco says fans shouldn't hold their breath for that possibility, now or ever. "I always imagined it might be in a nightmare sequence," she says, "but nothing more than that."

Luckily for fans of Leonard and Penny's relationship, Galecki is confident for a reunion down the road. "I think they'll stray and then rekindle with newfound lessons and love and newfound confidence," he says. "I hope so."