Kristin Cavallari Seen Leaving Cabo With 24-Year-Old New Boyfriend

Kristin Cavallari's wasted no time leaning into her new relationship with Mark Estes ... in fact, the lovebirds have already wrapped up their first getaway in Cabo together.

Check out these pics ... Kristin and her 24-year-old boo were spotted Wednesday rolling their suitcases to the American Airlines priority desk at the airport -- and the reality star was rocking a casual matching black set ... ME opted for a cozy hoodie.

They're not really flashing the biggest of smiles here -- if anything, you could say it's kinda the opposite -- but it's probably just the post-vacay blues kicking in ... Cabo can do that to ya. Plus, traveling tends to wear folks out ... so their mopey moods are nothing to fret.

While their vacay is over ... it seems Kristin and Mark are still very much in the honeymoon phase. In fact, on Tuesday, Kristin went full-on IG official with Mark, declaring how happy he makes her in a super cute selfie.

This came shortly after we got photos of them heading on down to Mexico together last Friday ... remember, this was supposed to be a business trip for Kristin, but Mark decided to tag along. So, a little work and play, it seems!

We've been told Kristin and Mark have been enjoying each other's company for about a month now -- and things are clearly moving along swimmingly between them.

Kristin definitely has a thing for those hot dude model types. She previously dated Tyler Cameron after her marriage to Jay Cutler ended.