You didn't really get to see all that much thanks to the poor angle, but the few milliseconds of cleavage you did get would easily be enough to last you the rest of the night. As you stroke it in the cold, you feel grateful to your friend and GF for helping you stay somewhat warm
After falling asleep on the beach beside your GF, you wake up to her casually chatting with your friend while he undoes her top. You notice they're both sitting on your towel and your cock involuntarily twitches when you imagine having to clean out the wet spots they're leaving.
Your friend thrusts with a bit too much force and the window slams shut, knocking you off. Even in the thorny bushes below, you can still sort of hear them plap if you listen hard enough. It might be a bad idea to fall asleep in the cold, so you focus on the noise to stay awake.