Jessica Simpson Furious: Nick Lachey and CaCee Cobb Canoodle

Jessica Simpson is reportedly furious as she feels she has been betrayed by estranged husband Nick Lachey and her best friend CaCee Cobb, Life & Style magazine is set to report.

CaCee and Nick play in the pool

It all began innocent enough, reportedly it was a typical evening at Level 3 nightclub in LA on Jan. 29.  But then a closer look at a canoodling couple reportedly revealed Nick and Jess BFF CaCee getting a little too close.

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An eyewitness was stunned to get a closer look: Nick, 32, was canoodling with CaCee Cobb, 27, personal assistant and longtime best friend of Nick's ex-wife, Jessica Simpson, the magazine will report.

"The two were all over each other," says the eyewitness, who knows both Nick and CaCee.

"Nick had his arms wrapped around her, and he was kissing her all over the side of her face and neck. Her arms were around him, too."

A second witness at the bash, thrown by Wilmer, confirms the account.

"We were watching in total disbelief," says the witness. "We kept waiting for them to rip each other's clothes off." The kissfest occurred around 1:30 a.m. and lasted just a few minutes, but "they were flirting the entire night," says the first eyewitness.

As Nick, in a button-down shirt and jeans, and CaCee, in a tight black dress and leopard pumps, steamed up the room, onlookers were shocked. "There may be nothing going on between them, but it was inappropriate behavior. Everyone was like, - "Wow - what are they thinking?"

The real question will be - what does Jess think.  Reports from the tabloid say she is crushed and blaming herself. 

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The report details that when Jess, 25, first heard the news about CaCee and Nick's PDA, she viewed it as a devastating act of betrayal - both by her ex and her closest friend, whom she turned to for support after her split. "I just can't see her doing this," Jess told a friend.

"Maybe she was really drunk and Nick took advantage of her. How badly does he want to hurt me that he would use CaCee like that?"

Then, sadly, Jess began to blame herself. "If it happened, it's my fault," she said. "I guess by letting her stay so friendly with Nick, I basically gave her the keys to the bedroom door. I'm going crazy now. Do you think it's really true? Why is everyone out to hurt me?"

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Life & Style notes that Nick's rep strongly denies the story. "Nick and CaCee are friends, that's it," says the rep.

--Cris Bergman