Mariah Carey is reportedly ''heartbroken'' over her separation from Nick Cannon but blames his insistence on working so hard for their problems.

The 'America's Got Talent' host has confirmed he and the 'Hero' singer - who have four-year-old twins Moroccan and Monroe together - have been living apart ''for a few months'' and friends blame his heavy work load for the separation. A source told E! News: ''She is heartbroken.

This has been going on for months. It has a lot to do with Nick's career choices. He does not have to work, but he's been throwing himself into gigs and projects. ''She has tried and tried to get him to stay home more, but he always uses work as an excuse. ''When she points out that, financially, he does not need to be working as much as he does, it p****s him off and pushes him farther away. He hates when people assume he's living off her money.''

If they do make the split permanent, Mariah, 44, is expected to base herself in New York, while Nick, 33, wants to be in Los Angeles, meaning they could face a battle over the care of their children. The source added: ''She wants to be in NYC full-time, but he's been wanting to spend more and more time in L.A. ''If and when they split [for good], she intends to stay in NYC with the kids.

She will fight for the kids. She is totally focused on them.'' Nick recently vowed his ''main focus'' was on the twins when he confirmed he and Mariah had been having problems. He said: ''There is trouble in paradise. We have been living in separate houses for a few months. My main focus is my kids.''