A source tells ET, "Scott has been having a hard time with Kourtney and Travis' marriage, but he is doing as well as he can be."
"He has mixed feelings because he loves Kourtney, but he also knows she is very happy," the source shares, adding that Disick "has a lot of regrets about how he treated Kourtney during their relationship."
Disick and Kardashian share three children -- Mason, 12, Penelope, 9, and Reign, 7. The pair called it quits in July 2015, after nearly a decade.
According to the source, "Scott and Kourtney's kids are happy, but naturally, always hoped that there was a chance their parents would get back together."
"Scott is sad that he isn’t as close with Kourtney or her family as he once was. He misses them all and wants to be included in things," the source says. "Scott still has a good relationship with the family overall, but it's a little different now. Kris is still like a mom to him and he loves her like his mom. He’s also still very close with Khloe."
Meanwhile, a different source tells ET that the newly married reality star "couldn’t be more in love and happier" following her wedding to the Blink-182 drummer in Portofino, Italy, over the weekend.
"She loves saying and signing her name as Mrs. Barker and everyone is so happy for her. She is so excited to be married to Travis," the source shares. "She knows she went through so much with Scott for years and she’s emotionally done. She spent years crying and worried about him, but she's focused on her next chapter."
The source says that Kardashian knows Disick "will always be in her life since he is the father of her kids," however she "feels like she is a better mom and person now with Travis. She isn’t going to let Scott's feelings ruin her moment."
The famous family hosted a red-carpeted ceremony at Villa Olivetta, a home on the idyllic Portofino estate of Domenico Dolce and Stefano Gabbana. The full Kardashian-Jenner entourage came decked out in luxurious Dolce & Gabbana attire.
Kourtney and Travis first exchanged vows in April, when they held a late-night ceremony in Las Vegas following the 2022 GRAMMY Awards. The couple then legally tied the knot with only a few witnesses in a California courthouse earlier this month before heading to Italy for this celebration.