Charlie Sheen & Brooke Mueller -- NOT Getting Back Together

Charlie Sheen and Brooke Mueller looked as cozy as two people can be this weekend in Mexico (see above) -- but Charlie tells TMZ ... they're still just "good friends trying to be great parents."

As TMZ first reported, the former couple went south of the border this weekend -- Charlie decided to take Brooke as a sort of "birthday/you're doing great in rehab" present.

But no matter how good they look together in the pics, Charlie tells us a romantic reconciliation is not in the cards. In warlock speak, Charlie says they are simply "working on mending the bridges, replanting scorched earth. The goal is harmony."