Nas & Kelis -- Romantic Getaway, Minus the Romance

Nas and Kelis insist they aren't getting back together, but they were out this weekend at the very romantic and luxurious Bacara Resort & Spa in Santa Barbara, CA with son Knight.

As TMZ first reported, Nas says he and his ex are becoming friends -- following a nuclear divorce -- for the sake of their 3-year-old son.

Our luxurious spies tell us .. Nas and Kelis were having lots of fun ... getting along great ... BUT nothing seemed romantic.