The vehicle could represent your body (as per the dream dictionary) and the dream perhaps represents your currents thoughts regarding sexual encounters. My guess is that you are reliving your encounters with your ex through your dream. Eitherways as sweetslumber put it, you got lucky

I've had similar dreams and I land up spending the whole day in an amazing trance. It's like youre on cloud nine.
Enoy the feeling

and hope this helps some.
Cheers!