I remember several times taking new girls, or existing girlfriends, with my best friend at college, back to our shared room for a fuck. It was never quite dark so we were aware of each other doing the business; particularly if one of us came first we would watch the other bang the girl to the finish line. It was good, as others have said, sometimes to exchange partners, bang a girl just fucked by my friend and deposit another load in her pussy while my friend did the same to the one I'd had first. In those days, safe sex didn't have the importance it has now: the girls were all on the pill so we banged away bareback with impunity. On all these occasions, we both enjoyed it, as we hope did the girls. Fortunately we two men have about the same endowment otherwise one or the other would have been concerned about comparisons.