I Can't Stop Thinking About Her When We Sleep.

Every weekend my wife and I go to some friends house to play D&D. Now my wife works nights with one of them so they ride together and I spend the night at their place.
The problem is I find their daughter absolutely gorgeous. We are both in our early 20s, and just to me she is so cute. While my wife is at work me and her talk and just while we talk I can't help but think of situations where we would maybe have sex, or kiss. Not to meantion the dreams and the fantasies of bending her over the couch she sleeps on and just railing her while my wife and her mom are working.
Me wife knows that I have these thoughts of her and she just uses it against me for fantasies, reminding me of just how much id love to see her pretty mouth wrapped around my dick or how I'd love to have her ride me.
I feel so guilty about these thoughts, but my wife encourages it, and my gods she is just a fucking bombshell of a gal...