If I'm being completely honest - my deepest, darkest, and most perverted fantasy of my wife:
She is either blackmailed into sex and forced to fuck, or raped. But she ends up enjoying her assailant's thick meaty cock and she cums! And she enjoys it so much so that she ends up submitting and then sucking him off until he cums in her mouth and she greedily swallows. Then she comes home, tells me about all the dirty little details and asks me to tie her up and invite a stranger over to reenact everything with her.