Kristin Cavallari, Jeff Dye Enjoy Steamy PDA in Mexico

Kristin Cavallari and Jeff Dye still won't officially say they're dating, but their lips are making it abundantly clear during a Mexican vacay ... they are definitely a thing.

Kristin and the comedian were all over each other in Cabo San Lucas ... kissing, hugging and laughing constantly. The only time they seemed to take a break from the PDA was to sip a drink while hanging with friends down south.

While they're openly enjoying each other's company it still seems like Kristin's trying to keep this unofficial-relationship on the DL.

For starters, she posted a pic on Instagram but didn't tag Jeff ... and did the same when she posted an IG Story with a couple of friends on the trip.

BTW ... she's wearing the same pink bikini on her Instagram post as the one she wore while out with her apparent new bae.

Kristin, who back in April announced she and Jay Cutler are getting divorced, was first seen hanging out with Jeff in Chicago in October making out, then in Nashville in November. Before reportedly meeting up again at Craig's in Los Angeles.