But Disick's latest conquest, 20-year-old model Christine Burke, has 37-year-old Kardashian especially livid.
"Kourtney was aware he was dating her, but never thought he would be so obvious in public, so soon," an insider told RadarOnline.com of the pair, who put on plenty of steamy displays of affection while out and about together in Cannes, France.
"Kourtney was holding on to a glimmer of hope that when he went to rehab that they could work on things at some point when he got healthy and maybe reconcile," continued the source. "But instead of focusing on sobriety, he just went out and got a girlfriend."
And one that is a dead-ringer for Kardashian's little sister, Kendall Jenner!
"She's annoyed about that," revealed the insider, noting Kardashian "is certain it's not going to last" between the new couple.
In the meantime, added the source, "Kourtney is just really upset at how open Scott is about this relationship."
As RadarOnline.com reported, this isn't the first model Disick, 32, has been spotted with since he and Kardashian called it quits on their nine-year relationship last summer. The bad boy dad has been linked to a series of stunners, including Megan Blake Irwin and Instagram star Indy Clinton.