Hi Teddy01, You say you are in a good stable relationship, So it's pretty obvious your wife is very content with just having sex with you.
You should be very happy about that as its a compliment to you. As you say it's your fantasy to see your wife with another guy.
Tread very carefully along the lines you take as you could actually turn something that is very good for you at the moment into something you may never dream of happening.
As you have already sugested this to your wife and she is'nt really particualy interested,Try as SVEN said with a few porn movies which include 3somes and 4somes ect.
If your wife does get interested maybe try a 3some first and see how it pans out. What if you did this and the guy your wife was fucking turned your wife on more than you ever have. How are you going to feel about that???
So it may be best left as a fantasy unless you are positive you are not a jelous type of guy. Also do you only want to watch or join in with another guy?
A women can have some of the best sex going with two guys together,but she has to want that.
If your thinking of another couple your wife might not want to see you with another women. It can be a very dangerous game to play, as you have said you have a great relationship but you's have not been down that road.
Personally if you get your wife to come around i hope it all works out well, but i would give it alot of thought before you keep pushing the point to her..
I have personally been in a 3some where the guy wanted me to join them for some hot sex. Later after a week or so he wished he had not done this as she wanted to do it more and more often with me, get the point.
So that actually ended his relationship with her, yes it's probably a pretty rare situation but trust me it does and can happen.
On the other hand i have been in quiet a few 3somes and 4somes where everybody had a great time, as i said i believe a women can have the best sex with two guys together, only if thats what she wants and knows there will be no problems after the nite, so take a little advice from the people above before you push someone away who seems very much in love with you. Only my thoughts, and i'm certainly not bragging or anything like that. Good luck either way you venture.;D