I remember about a similar topic in other forum.
Some one posted a similar topic, and my answer was that i don't like that idea and most men i know won't like it either. But later some one else told me that it was wrong for me to say that, because is similar to say: "i don't like it and you shouldn't either".
So, maybe it is truth that many people don't like the idea of seeing her g/f having sex with some one else but does not mean that there is something wrong with you.

There is nothing wrong with it.
I prefer to daydream about stuff I could do to her and what she would do to me but everyone is different.

Have you ever thought of having an orgy/threesome with her and another guy.

Since you said your heterosexual I mean you both f*** her and not each other just to clarify.

You can always bring it up in a joking kind of way and if she says shed like it you can talk about it more seriously.

As the saying go whatever floats you boat.

You're normal...i get this too...its the voyeur in us all.

I think its part of the mentality that we like to be able to please people. Not in a sucking up way like you do in skool and work...but to give people pleasure...comfort etc...

And from it...you get pleasure too albeit not in a direct way. 'Takers' won't understand.

If you want to suggest this to here...that's another problem...

We all fantasise! About sex, money, fast cars, whatever. A fantasy is just that; something you may never possess or do  - but that you wonder about (what it would be like).

You are honest about yours, and that's good. Many people don't acknowledge (or they even actively try to "bury") fantasies that might be considered socially unacceptable.

Just because you have a fantasy doesn't mean you would ever necessarily really want to see it in reality - for most people it is just for kicks (although the fast cars and being rich DOES sound good!) . Bottom line is - a fantasy is just a fantasy - don't beat yourself up over it, just enjoy it for what it is!

I dont think that you have a problem, that is your preference, everyone has a fantasy whether it happens or not, its a fantasy and you can't help it, hope things go well with you good luck.

I'd say that's pretty normally considering i've at one point thought about the same thing although at the same time I thought if it ever actually happened i'd kill the guy.