Both Dannii and Kris, who have a two-year-old son, Ethan, have been linked to other people since their split in March.
Last week it was reported that Kris was getting cosy with former Miss England finalist Sara Beverley Jones.
Meanwhile, an Australian newspaper reported that Dannii had snogged 24-year-old Aussie singer Johnny Ruffo – claims that her publicist vehemently denied.
But, according to our source, despite them both denying that they are dating other people, Dannii, 40, and Kris, 33, are struggling to cope with their jealousy.
An insider tells Reveal: "Dannii is still in love with Kris, there's no doubt about it. But the stories linking him to Sara just do so much damage.
"They both have feelings for each other so it drives them wild with jealousy any time there is even the mildest hint of anyone else on the scene."
Following their split in March, Kris admitted things were hard, but insisted they were still "the best of friends".
Despite remaining amicable for the sake of Ethan, their relationship became strained after a biography of Simon Cowell claimed that Dannii had an affair with the music mogul.
Although it happened before she got together with Kris, we told at the time how the male model was furious that Dannii had never told him.
Last week, for the first time ever, Dannii acknowledged claims about her affair with Simon, saying: "I haven't read the book, but I've ben told about the excerpts that relate to me, and the speculation about my private life… they looked very pleased with it at their launch. I'm sure if makes for a great read."
Read the full story in this week's Reveal magazine. Out now.
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