A source told People that Richie ended things after Disick was with someone else, with the insider sharing, "He cheated on her, and she confronted him."
Another source previously told the magazine that Disick's "old issues" also contributed to the breakup.
"When Scott drinks, he is a sloppy mess and fools around," the insider said.
On Thursday, Disick was spotted looking cozy with a mystery woman at Kanye West's YE listening party in Jackson Hole, Wyoming. TMZ reports that Disick was overheard saying he was single.
The pair's breakup news came just days later and was a surprise to many as the couple had just recently vacationed together.
One source told E! News that Richie broke up with Disick due to his "toxic behavior."
"Sofia broke up with Scott after the pictures and rumors of his behavior in Wyoming were floating around," the source said. "She couldn't take it anymore. Scott has been off the rails recently and is not in a good place. He goes in waves of partying really hard and then will have his good days and it's just very toxic behavior. It's very up and down."
Richie's father, Lionel Richie, was also reportedly not a fan of his daughter's relationship.
"Lionel hasn't approved of the relationship since the beginning," People's source said. "He joked about it publicly but he was livid."
Another source previously told People that Lionel "thinks Scott is the worst person she could ever see and that he raised her better than that."
"He thinks she should have more respect for herself as a young woman. Lionel knows Scott's playboy ways and he doesn't want to see his daughter get hurt," the insider added.
Despite the reports, a source said that the pair could potentially reconcile.
"It's likely not totally over," the insider said. "They've broken up multiple times since they started dating and always ended up back together. No one would be surprised if they're out again together in a few days or weeks."
Sofia and Disick confirmed their relationship in September, recently taking a tropical trip to St. Barts that saw Sofia with Disick a happy birthday on Instagram.0comments
"Happy Birthday babe!" she wrote. "Thank you for being you. Love you."
Photo Credit: Instagram / @sofiarichie