6:48 PM PT -- TMZ has just obtained photos of Kristin and Mark at the Nashville bar last night.

As we told you earlier ... our sources tell us they are just friends and not back together.

Kristin Cavallari seems serious about wanting to remain friends with ex-boyfriend Mark Estes, because they recently hung out together ... at one of their old stomping grounds.

Sources familiar with the situation tell TMZ ... Kristin was out with some friends Wednesday night on Broadway in Nashville ... at the same watering hole Mark also happened to be at with some of his friends.

Folks who were there tell us Kristin and Mark were spotted together at Kid Rock's Big Ass Honky Tonk Rock N' Roll Steakhouse.

With Kristin and Mark at the same location, our sources say the exes ultimately ended up hanging out together ... talking at the bar.

Unclear if Kristin and Mark just happened to be at the same place at the same time, or if they communicated their plans prior to going out ... but our sources say they are not back together romantically and are just friends.

As we reported ... Kristin called it quits with Mark back in September after 7 months of dating, with the 37-year-old reality star explaining age was a factor in her split from the 24-year-old.

When they were together, Kristin and Mark spent some time going to bars on Broadway -- like many folks in the Nashville area -- so there's a history here.

Kristin's on the record saying she would like to keep Mark in her life in some capacity ... and it looks like that's happening ... at least for now.

We've reached out to Mark for comment, but so far no word back.