Wilmer Valderrama & Minka Kelly -- Old Habits Die Hard (PHOTO)

Wilmer Valderrama and Minka Kelly fell right back into their old ways this weekend ... only this time they did it in Mexico.

We got the two actors together in Cabo Saturday after a day of lounging in the sun. Come nightfall though, they made off together ... to somewhere.

Wilmer seems to have settled into a new groove since splitting from Demi Lovato in June.

Demi too.