Heidi & Spencer -- Busted in Costa Rica!

Heidi Montag and Spencer Pratt are getting divorced and Spencer is threatening to release a flurry of sex tapes that  feature his handiwork with Heidi, along with some girl-on-girl ... so it's more than telling that a paparazzi agency shot video of the two of them together Sunday at a resort in Costa Rica, frantically separating so they would not seem in cahoots.