After being with my girlfriend for just over 3 years I have started to have fantasies about her being fucked by another man or woman. From before we were together I know that she had a lot of sex when being a student. However over the last wife's years although we have and still do have mind blowing sex the thought of her cumming because of somebody else has started to turn me on. I have never suggested anything like this to her? How do I bring it up and get to see my fantasy come true?