The couple of nearly a decade, who have three children together, split over Fourth of July weekend when Disick was caught getting touchy-feely with ex-girlfriend Chloe Bartoli in Monte Carlo after spending a month away from home, E! News reported.
Kardashian, 36, "is putting on a brave face," a source told E! News, "but she is over it. She's fed up. It's humiliating and disrespectful. How much more is she supposed to take?"
"Kourtney has always taken Scott back and been by his side, but now with three kids it has gotten old," said another source. "Kourtney has to do what's best for the kids."
This past holiday weekend, Disick, 32, was photographed with Bartoli, 25, a handful of times and the physical intimacy between them could not be ignored or exaggerated. Disick was caught caressing the LA-based stylist's head and back, while she snuggled up to him at the beach and fed him pasta off her own fork at dinner.
"Scott has been running around saying he's single," a third source noted. "Kourtney dumped him after she saw the pics [in Monte Carlo] and he hasn't been home after a month-long party binge."
Kardashian and Disick have dated since 2006 but temporarily split in 2010 prior to her pregnancy with son Mason, 5, due to Disick's alcoholism. Disick then had a brief yet "hot and heavy" fling with Bartoli during his separation from Kardashian, but he reportedly reconciled with the reality TV star by the end of 2010.
"She really has had it this time," an insider toldUs Weekly.
Sources told TMZ that Disick already knew his relationship with Kardashian had ended, which was why he was absent from home for weeks and had been telling people in Monte Carlo he was "newly single."
A representative for Kardashian reportedly declined comment.
Disick has been hanging out with buddies who "are not a good influence" and haven't been "looking out for his best interests," according to E! News. He's allegedly in worse trouble than ever before, partying hard and drinking heavily in a downward spiral.
Disick had an eye-opening experience when entering rehab in 2014, but he relapsed this year and sought treatment in March at a facility in Costa Rica. He returned to California a few weeks later but was reportedly expected to return and continue therapy.
Kardashian seemed extremely supportive of Disick when he was making real progress, saying she was proud of him for focusing on himself and changing the error of his ways. The pair's three children are a son Mason, 5, daughter Penelope, who turns three-years-old on Wednesday, and a son Reign, six months.