"Kristin knew from the beginning that Jay was not seriously interested in Jana," the source claims, alleging, "He was more interested in making Kristin jealous." ET has reached out to Cutler for comment.
Cavallari and Cutler separated last April after 10 years together. They share three kids together; 9-year-old Camden, 7-year-old Jaxon and 5-year-old Saylor. The source says Cavallari "is focused on her own life, her businesses and taking care of her children."
"She is happy and doing her own thing. She isn't caught up in who Jay is dating, but she did think it was shady of Jana to go out with Jay," the source claims. "Kristin thought they had a friendship and felt like she had been supportive of Jana through her own divorce."
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Kristin Cavallari on Spending Quality Time With Her Kids Amid Quarantine and Jay Cutler Divorce
Kramer's divorce from her ex-husband, Mike Caussin, was finalized in July. Last month, romance rumors between her and Cutler sparked after it was reported that they were going on dates in Nashville, where they both live. At the end of the month, the two posed for pictures together during a night out and didn't leave each other's side.
A separate source previously told ET that the former Laguna Beach star blocked Kramer on Instagram after she went on a date with Cutler because she had previously thought of Kramer as a friend.
"Jana and Jay did go out on a date in Nashville," the source said at the time. "Kristin believed that her and Jana were friends and has blocked Jana on Instagram in response to this happening. Kristin is moving on and doing her own thing."
However, a second source told ET that Kramer and Cavallari are not close, saying, "Jana has never thought of Kristin as a close friend and only as an acquaintance who she has met a few times."
"I know my truth, I know my heart, I know the person that I am, and I can go to bed knowing those things," Kramer explained. "I don't feel like I have to defend -- I don't wanna defend myself anymore. I know who I am, I know my intentions in my heart and I have respect for everybody involved. So as long as I do things the right way, then I'll be OK."