There's fantasy's you tell your spouse then there's the ones you keep to yourself, and this is one of them.

Essentially I want to see my wife who is without a doubt faithful to me, and would never do anything behind my back to hurt me be seduced.

Ideally I would be watching from somewhere I wouldn't be seen but could see everything happen, like we've happened to host a house party and the last person left at the party knows exactly why he's there and it's to seduce my wife while she thinks I'm "passed out" in our bed.

Watching as he slowly breaks her down untill she's acting like a complete slut for him in our living room.. there's no better fantasy for me then that.