Well, you were VERY wrong ... and these pics of the Pistons superstar's girlfriend in a skimpy white bikini is all the proof you need.

Of course, BG's special lady friend is Francesca Aiello, who founded Frankies Bikinis ... so, this is kind of her job. Man, she's good at it.

The new couple hit Miami Beach on Friday morning ... both showing a LOT of skin and gettin' all romantic in the water -- almost like that scene from "Dirty Dancing."