Jessica Simpson (search) and Nick Lachey's (search) life used to look like wedded bliss. The pop-music couple seemed perfectly matched on the first two seasons of the MTV hit "Newlyweds: Nick & Jessica." (search

But in the reality show's third season, which starts tomorrow, it looks like there's some trouble in paradise.

Last season, much of the show's tension came from Lachey's jealousy, as Simpson's singing career took off and his seemed stuck in first gear.

But this year, the long-suffering former boy bander has to cope with CaCee Cobb, Simpson's best friend and road manager, who moves in with the couple while she's looking for an apartment.

CaCee (it's pronounced like "Casey") also comes from Texas, and she and Jessica quickly become inseparable, going out to shop while Nick is left at home to watch basketball on TV.

"In one episode, he goes into the bathroom and finds a picture next to Jessica's tub," says the show's producer, Rod Aissa.

"You'd figure it's a picture of him and Jessica, but he picks it up, and it's actually Jessica and CaCee."

Later, after Nick takes Jessica out for a romantic dinner, Jessica tells him that she loved the restaurant -- so much that she wants to take CaCee there.

Meanwhile, CaCee's apartment search seems to be a non-starter, even after Nick takes her hunting.

"He keeps making jokes about evicting CaCee," Aissa says. "He turns into a real curmudgeon."

One day, when Jessica and CaCee are gossiping about a visit to a psychic, Nick asks CaCee if "your psychic said you'd be living rent-free for a year."

"Poor Nick," Aissa says. "Can you imagine your wife's best friend moving in?"

And that's not the only problem the couple is facing, as we discover in an episode when Jessica berates Nick for not opening her car door.

"You always opened doors for me when we first got married," she says.

"Well, when we first got married," he says, "I was getting laid."

Then there's the issue of whether or not they're going to have children, and from the look of things, we shouldn't hold our breath.

In one episode, they wind up babysitting for a friend's infant -- and it's a disaster.

"The best part was when they had to change the diaper," Aissa recalls.

"The look on Jessica's face was priceless.

"It was panic and disbelief -- like, 'Oh, wow, I forgot that this happens with babies.'"

It's the sort of dumb-blonde moment that Simpson has practically patented over the last two seasons. (Remember when she called a "platypus" a "platy-mu-pus"? Or when Lachey offered her some Buffalo wings, and she told him she didn't eat buffalo?)

The third season of the "Newlyweds" will be full of more sure-to-be-famous Jessica non sequiturs -- including, in the first episode, her asking if male ballet dancers are called "ballerinos."

That's ditzy, for sure. But we can't get enough of it. Simpson is everywhere these days, touring the United States to promote her latest album, "In This Skin," which has already sold almost 2 million copies. She'll sing at Radio City Music Hall this Friday.

Simpson also recently signed up to play Daisy Duke in an upcoming film version of the '70s TV show "The Dukes of Hazzard," and although ABC did not pick up a sitcom that she worked on last year, they did hire Simpson and Lachey to do eight more variety-hour specials over the next two years.

The third season of "Newlyweds" has been filming off and on for about four months now, though Simpson and Lachey are taking a break while Simpson is on tour.

"It's so great not to have cameras follow every single move you make for once," Simpson says. "It gets hard."