I have never really fantazised about someone else while I was having sex with my partner. I am always very involved in the present to think of anyone else.

For my solo play, I'll fantazise about many things, and I don't feel bad about them at all, even if it does not involve my significant other (when I have one).

But, I would feel uncomfortable knowing that my partner thinks of someone else when he's having sex with me. I am ok with the idea of him fantasizing with a female celebrity when I am going down on him and he's appreciating the moment, but not with a woman he knew personally. That's where my jealousy kicks in. There is less chance that he would be tempted or have the opportunity to act on the fantasy.