Disick, 32, hasn't been at their Calabasas home in a month, "solid" sources told TMZ, and
"His partying lately has made her make this tough decision," one source told the website.
Insult to (Kourtney's) injury: On Thursday, Disick was photographed in Monaco looking very cozy with stylist Chloe Bartoli, reportedly an ex-girlfriend. An Us Weekly source predicted Kardashian would "freak" when she saw the pictures, while another said the two were "were all over each other and so blatant," and that he was a "drunken mess."
In June, he was photographed in New York City with another brunette at what appears to be a hotel-room party, Us reported Monday, with a source suggesting they'd spent that night together.
"Kourtney has always taken Scott back and been by his side, but now with three kids it has gotten old," a source told E! News, which is affiliated with the network that airs "Keeping Up With the Kardashians." "Kourtney has to do what's best for the kids."
Another source told E! that the self-proclaimed Lord Disick has, while on his alleged one-month party bender, been telling people he was single.
"He acts out, he rebels, he drinks too much and he embarrasses her," a People source explained. "He acts like a kid sometimes. He just rebels against the crazy responsibility of having three kids and makes Kourtney do it all."
Disick checked into a Costa Rica rehab facility in March but reportedly left after just a week. His partying has split them up before, but they reconciled after he quit drinking temporarily and they went to counseling.
Their third child, Reign Disick, was born Dec. 14, 2014. Reign's big bro Mason is 5, and big sis Penelope turns 3 on Wednesday.