Kristin Cavallari isn't rattled by her ex, Mark Estes, hanging out with other women ... even after his joke proposal to Liv Walker.

Sources with direct knowledge tell TMZ ... the "Laguna Beach" alum isn't bothered by Mark spending quality time with different women, as their relationship was done for good back in September.

KC and Mark have no plans to reconcile romantically, so she respects the TikTok star's decision to get back out there after their split.

We're told Kristin is fully aware Mark will be seen out or on social media with women ... and it doesn't bother her one bit. Kristin also plans to start dating again soon ... so, he'll eventually have to see her doing the same thing.

This comes days after Mark was spotted spending quality with the "Love Island USA" star ... who he jokingly proposed to after mingling at a Nashville bar.

While the engagement wasn't sincere, their connection seemed to be palpable ... Mark and Liv were later spotted together at a different bar in Nashville.

However, Kristin and Mark had their own night out in Music City last week ... though, we're told there wasn't a romantic reunion in any way.

Sources say it was strictly a friendship hang after they bumped into each other at a bar in the area. We're told Kristin had been in Nashville to see the Billie Eilish concert with friends ... she did not originally plan to link up with Mark.