This whole sexual fantasy thing with my wife started a year or so ago when I found a photo on the Internet that looked like my wife posing half nude on our master bedroom bed. I went through various emotions and eventually felt I had to know if it was her. I worked up the courage one Sunday morning to show the photo to her and of course she was a bit upset and said it wasn't her. She chastised me for doing too much Internet and for even "thinking" that she might do something like that. She seemed sincere and I believed her. We wound up going to the master bedroom and making love and that's when I realized that though she might have been pretty upset, more importantly she was extremely aroused as well.
It was during that lovemaking that I also worked up the courage to confess the strange mixture of emotions that had been stirred up in me by the thought that she had posed naked for someone else. That was the first time I shared my fantasy with her of watching her with another man and how it turned me on and made me jealous all at the same time. She first seemed a bit scared, then amazed (as though I had lost my mind), but I could tell she was getting more and more aroused at the same time. During that lovemaking she got more aroused than I had ever seen her and soon had the most intense orgasm I had ever seen her have to that point in our marriage.
After that experience I decided to introduce the fantasies to arouse us both and set the stage for more of those awesome climaxes. It took a while to introduce them gradually and on occasion I faced some stiff resistance. But, over time I also explained more about my fantasies; at least what little bit I understood, myself. My wife became more understanding within limits and became less resistant to the fantasies. She even to some extent accepted the reality that the fantasies did indeed turn her on and contributed to her ability to enjoy our lovemaking. As a result of all this, SEX between my wife and me has never been better and she's never been a more desirable woman to me.