He won't be a slave for her!

Britney Spears' constant demands that fiance Jason Trawick "check in with her" have him fuming, a source tells Us Weekly.

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"The romance is gone," says the insider. Trawick, 40, "puts her on speakerphone so friends can hear her nagging."

(A rep for the X Factor star, 30, denies this, and an insider insists, "That's not Jason's style. They're happy.")

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But the source contends there's turbulence ahead: "I'd be shocked if they got married."

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Spears, who is a mom to Sean Preston, 7, and Jayden James, 6, (with ex-husband Kevin Federline) got engaged to Trawick in December 2011, but have yet to set a date.

This article originally appeared on Usmagazine.com: Jason Trawick Mocks Fiancee Britney Spears!