MARIAH CAREY’s $500 million divorce from NICK CANNON has exploded with mutual claims of cheating behind the scenes, sources say.

While Nick confirmed Aug. 21 that he and Mariah were “living apart and there is trouble in their marriage,” The ENQUIRER reported almost a year ago that the marriage was on the rocks amid cheating allegations and rumors that Nick was ready to go after his superstar wife’s fortune.

In Oct. 2013, we reported the diva, 44, had taken off her wedding ring, and Nick was livid she’d been “flirting up a storm” with rapper Nas.

We also reported Mariah had a “one-night stand” with rapper Young Jeezy in 2008 – the same year she married the now 33-yearold “America’s Got Talent” host.

Sources say the couple – parents to 3-year-old twins Monroe and Moroccan – were also fighting over Nick’s bid to hook up with former contestant Lys Agnes, 27, in 2011.

A source told The ENQUIRER : “There’s dueling claims of cheating. Nick also infuriated Mariah by bragging on the radio that he’d slept with Kim Kardashian before they wed – and further boasted about other beauties, including Nicole Scherzinger and Christina Milian. “It’s going to be nasty.”

But Nick has denied there’s been infidelity in the marriage.

Meanwhile, Mariah is having a career, financial and emotional meltdown, according to another source. Along with recently firing her manager, Jermaine Dupri, the source claimed, “Mariah also dumped her longtime assistant Louise by shoving her out of a car in downtown Manhattan.”

Now Nick is under a “gag order” from Mariah from speaking further, according to a new report.