I've shared a woman plenty of times with another guy, a few times with two other guys. You don't really notice the other dude unless you are doing a DP to the gal, then you can't help but notice as his cock and balls are likely rubbing against your own.
I dunno, I get off watching a gal get fucked in porn scene by a dude....experiencing it in real life isn't any different. In fact, it helps to look at the other guy so that you can both get your "rhythm" going. When you are hammering her ass from behind and he's getting head, you wanna be sure you are pushing when he's pulling and vice versa or it gets all herky-jerky.
I love the standing DP in PORN, I've done it once in real-life and it just aint that comfortable, even with a featherweight. Too much weight on your cock and too hard to get the rythm right. But in a porn flick, it's hot. I love the camera angle from below and the look on the girls face while it's happening....kinda like "no escape so I gotta take it," very
_________________________
Darrah Ford's family video archives - Father's Day, 1996: