Heidi and Spencer Pratt Jet Ski in the Bahamas

Spencer and Heidi Pratt are closer than ever ... based on the hip to hip action they're getting down in the Caribbean.

The ex 'Hills' couple looks to be having a blast jet skiing and hanging on the beach in the Bahamas. No one thought they'd last, but check 'em out almost 10 years later still together ... still as thirsty as ever.