My dirty fantasy that I sometimes get off to is where like a poster earlier mentioned "imaginary spouse".
It's based on a re-occuring theme from a now cancelled tv series called "Magic City"
https://en.wikipedia.org/wiki/Magic_City_(TV_series)
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In it, Mob boss Ben Diamond has a sugar baby type wife (ala pres. trump's wife). Hot as fuck but he's an old fat ass.
he has a one sided (sort of like a police interrigation room) glass ceiling where he watches and gets off to his hot wife getting fucked by one of the younger characters in the film..
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For whatever reason with me, for the past 2 or 3 years it's been a dark fantasy of mine where I'm married to this girl I had a serious crush on in college and as the traveling, over-stressed man that I am, I've come to grips with the fact that I cannot with consistency satisfy this younger (not too young she's in her 30's), hotter wife of mine so I'm turned the fuck on by her seducing younger men. From tease play - her grinding against their crotches and leaving them with stiffies to her all out fucking them like those cougars in porn vids. The fantasies are so bizare but hot to me as I prefer her to go full GFE when fucking the guys b/c I'm aware of how much it would turn me on as a younger man to have a married smoking hot cougar seduce me and suck me bare.