The couple is reportedly co-habitating with their three children Mason, 6, Penelope, 4, and Reign, 23 months, at Kardashian's Calabasas mansion.
"Scott has been staying at Kourtney's house with her and the kids for the last few weeks," the source told Us. "He has really cleaned up his act and been well behaved. Kourtney is always skeptical about how long it will last, but she has been very encouraged to see how much he has been trying."
Disick and Kardashian's on-again, off-again relationship of nearly nine years was always strained due to his partying habits and substance abuse. Disick fell off the wagon multiple times despite seemingly-successful rehab stints.
However, as of recently, the reality TV stars have been amicably co-parenting their three kids and Kardashian has been impressed with her ex.
"They are planning to do everything together over the holidays with the kids and will see what happens," the source said with Thanksgiving and Christmas fast approaching. "For now, they are taking little steps in the right direction."
"Scott has always hoped he could win Kourtney back, and he did set up this trip," an insider previously told the magazine of their getaway.
"Of course he hopes one day she will see the light and come back to him. That's why he went to rehab [last year]. He has tried everything, but it's Kourtney who won't go there. I still think it could happen one day, but so far Kourtney has not been willing to go back there."
Kardashian, however, has never been able to truly let Disick go. She has always held onto hope they could reconcile at some point.
"The idea of having my family together is amazing, but it's not the way things ended up. They may end up there. I'm not sure. To me, it's in God's hands," Kardashian told Cosmopolitan magazine in August.
"If it's meant to be, then things will line up... We definitely tried for a long time. But relationships are exhausting! Being able to focus on the kids and me right now is good. We say to each other all the time, 'I'm the coolest ex-girlfriend/baby mama you could ever ask for!'"