The couple started dating in late 2002 after recording duet "'03 Bonnie & Clyde," but they remain furiously private over their relationship.
The 37-year-old said, "One day, soon--let's leave it at that."
When asked if he would consider marrying in Vegas, Carter replied, "I don't know. It's kind of comfortable here."
Carter is planning to open his third 40/40 nightclub in the Palazzo Hotel in Vegas in December.
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