the technical truth of it is this, a man and women together inviting a 3rd party is good at times but when its another guy this poses indifference in feelings relative to each or rather to both the man and women. the man will experience differences in the womans vagina not due to size difference but due to difference in sexual style the second penis will not perform the same as teh first and thus changes the physical feeling of the first . 2 women however there is no change except in teh difference in oral style. external pleasure is easier to compensate for than internal. if you dont understand than your not thinking hard enough
