Nicole Scherzinger and Grigor Dimitrov are "committed" to each other but the distance is making it difficult.
The 39-year-old singer and her tennis ace boyfriend are "frustrated" about having to spend so much time apart because of their jet-setting schedules.
A source told The Sun newspaper: "Nicole puts her heart and soul into X Factor and Grigor has a busy training schedule. They are committed to each other but are frustrated that their only real communication is on the phone."
It comes after Nicole revealed she would love to have kids in the next five years.
Sharing her ambitions, she said: "In five years time, hopefully I'll have a family. Touring, singing, creating movies, and a family. I wan to be like Sade, J. Lo, Bette Midler - all of them are still killing the game."
And the brunette beauty would love to get married "one day".
She shared: "I'd like to get married one day. I'm looking for a wedding, my wedding. I think the heavens will sing when I get married."
Nicole - who previously dated Formula One star Lewis Hamilton - believes she is a "fool for love" and says the "bravest thing" she has ever done is letting someone she loves go.
She shared: "My greatest weakness is - I'm a fool for love. A real sucker ... The bravest thing I've ever done is loving someone and letting them go when you know it's not healthy for you, or serving you. Then you're finally loving yourself."