LEANN RIMES is “losing it” over dread rival BRANDI GLANVILLE’s bawdy tell-all, making her second guess her nups to cheating hubby, EDDIE CIBRIAN.

Brandi Glanville’s tell-all “Drinking and Tweeting” has Lee Ann in a snit, a source close to the country thrush said, adding the salacious memoir is inflaming her fears about the strength of her marriage to Eddie Cibrian, RadarOnline,com reported.

“This is bringing out LeAnn’s nagging fears about Eddie that one woman isn’t enough,” a LeAnn insider told a weekly publication about the book, which goes into detail about Eddie’s unfaithful tendencies.

 “Does it bother her? Of course — no woman would want to read these things about her husband,” the insider said. “But she knows that Eddie loves her and she’s secure in that … LeAnn desperately wants to believe him. If they don’t last, she looks like the biggest loser in the world.

“LeAnn has always worried about Eddie being attracted to Brandi,” the insider said. “It was devastating for her to learn that Eddie didn’t leave Brandi, that he wanted both of them.”

The insider called Brandi a “toxic” person who “believes her own lies” and is “desperate for money and attention.”

 “That’s a dangerous combination,” the source divulged, noting the Real Housewives of Beverly Hills star has done her best to paint LeAnn “in the worst possible light.”

“That’s pretty good revenge,” the insider said.