'American Idol' Finalist Elise Testone -- Denies Being 'Other Woman' in Bitter Divorce Case

"American Idol" finalist Elise Testone is a no-good man-thief who broke up the 6-year marriage of an 'Idol' guitarist -- at least according to the dude's wife, but Elise tells TMZ she never did the deed.

Here's the deal ... Elise met Errol Cooney during Season 11 of 'Idol' -- when she made it to the top 6, and he played guitar for the band. Both Elise and Errol were on Idol's summer tour.

Just last week Errol's wife Erin Cooney filed for divorce in LA County Superior Court ... citing "irreconcilable differences" -- but a rep for Erin tells TMZ the real reason for the breakup is an alleged affair between Errol and Elise.

The rep claims ... back in September, Erin stumbled upon what she believed to be incriminating emails between Elise and Errol, and immediately confronted him.

The rep says Errol confessed to everything.

In addition, TMZ obtained an email Elise sent to Erin last week ... in which Elise says, "Errol was the only person who I felt really loved me in my entire life."

Elise also apologizes to Erin for "any pain you feel I may have caused you, but this is not my fault."

When we contacted Elise ... she denied having the affair, saying ... "We developed a friendship on Tour and he developed feelings for me."

Elise adds, "Their divorce has nothing to do with me and has been a long time coming." Attempts to reach Errol were unsuccessful.