According to a source, their six-year marriage is on the rocks and "has been bad for a while."
While Carey, 45, remains at the couple's Manhattan apartment with their 3-year-old twins Moroccan and Monroe, Cannon, 33, "has been staying in hotels."
So what went wrong between the pop diva and the America's Got Talent host?
Another source close to the couple – who surprised fans in 2008 by tying the knot in a secret ceremony just weeks after they began dating – tells PEOPLE that Carey's professional concerns may have contributed to the tension in their relationship.
"When things don't go well career-wise, sometimes you turn on your other half," the source said, referencing the disappointing sales of Carey's recent album, which was released in May.
"While she can be very down-to-earth and hilarious, she can also be high-maintenance."
And while the couple both released similar statements citing their continued focus on their kids, those around them fear a separation could get ugly.
"There is a lot to fight over," the second source adds. "It could get contentious."
Reporting by K.C. BAKER, LIZ McNEIL and MICHELLE TAN
For more on their relationship and a look back at their wacky romance, pick up the current issue of PEOPLE, on newsstands now