The 'Real Housewives of Beverly Hills' star - who has repeatedly blasted the 39-year-old actor for leaving her in 2009 for the 30-year-old 'Can't Fight The Moonlight' singer - reportedly enjoyed several flings during their eight year marriage.
A source told US Weekly magazine that the 40-year-old reality TV star also had sex with another man in their bedroom just six weeks after the birth of their youngest son Jake, now five.
The insider said: ''Brandi loves to play the victim but she doesn't tell the whole story.''
In her new tell-all memoir, 'Drinking & Tweeting and other Brandi Blunders', Brandi - who admits she still loves Eddie - claims she doesn't understand how the father of her two children found the ''extra energy'' to cheat on her with his now wife LeAnn because she thought they had a very fulfilling and loving marriage.
She ranted: ''Let's be clear. Eddie and I had an extremely healthy sex life (so where he got all that extra energy, I'll never be sure), but every so often we would run away together so we could make love in the middle of the afternoon. And he would kiss me the way he did when we had nothing but time.''
Her long-time rival LeAnn, who wed Eddie in 2011 after legally separating from her husband Dean Sheremet, is said to be ''shocked'' and in a ''fragile state'' after reading some of the excerpts from Brandi's book.