I am glad you raised this question. One thing that stands out in my mind going back to the first time my wife was ever with another man is the aroma and scent of their sex. It was overpowering and intoxicating for me. I have tried to explain this aspect of the night, but most men cannot identify with what I experienced.
Our first time was with my lifelong best friend. My wife initiated the action and, it was me who undressed her for my friend, and then at her instruction, I undressed my friend. At first, there was not any discernable aroma or scent detectable. He smelled of soap and clean and, my wife had a light fragrance of her Cool Waters perfume.
As they both became more aroused, I detected his salty, musky scent fill the room. His smell quickly overpowered the room, and I found it intoxicating. I could not get enough of their combined hormonal scents that were very distinct. I sucked his cock and ate my wife's pussy while he fucked her, and I loved it all. That scent and aroma still entice me today whenever my wife finds a new man or BULL.
I love to be underneath my wife when she takes a cock from behind. The sight of a man buried deep inside my wife's pussy, the scent of both their sex combined, the sounds of slapping flesh, and the taste of their mixed cum is the most fantastic thing in the world.