Pam Anderson's relationship with Kid Rock just got super-ROCKY because she thinks his ex-girlfriend Sheryl Crow is back in the picture -- and Pam is furious.

kid rock

The blonde bombshell and her boyfriend got into an ugly screaming match over Sheryl -- and she's given him an ultimatum to cut Sheryl loose or get lost!

The problems developed after Kid got together with Sheryl, 40, late last year to make a music video.

A concerned Pam knows just how fickle 32-year-old Kid can be. He dropped Sheryl in early 2001 -- right after meeting voluptuous Pam at a party.

kid rock

"Kid Rock and Sheryl have been in constant contact since early November because of their work on the video," an insider told The ENQUIRER. "And Pam is watching him like a hawk.

"That's caused so much tension between Kid and Pam that the recent holidays were a living hell.

"They bickered, then went to Tahoe for a couple of days to work things out.

"They flew to Detroit for New Year's, but they got into a nasty shouting match about Sheryl -- and Pam ended up flying back to Los Angeles early."

The 35-year-old former "Baywatch" star has told Kid he'd better watch his step -- or else!

"Pam has demanded that he cut all personal contact with Sheryl or their relationship is over," disclosed the insider.

"But he's fed up with Pam's jealousy and their fighting."

Disclosed a close source: "Kid's incredibly torn right now.

"He and Pam were once headed toward the altar -- now it remains to be seen if they will be headed anywhere together."