In the many years since I started having sex I've gone from one extreme to the other on this issue. I remember a time when I was young when I would have completely freaked out at the thought of my husband/boyfriend touching another woman, let alone actually having sex with her! Then at one point I was in a relationship in which we were becoming fairly hard-core swingers and the only thing that would have bothered me would have been if it had been behind my back.
It's difficult for people who have never been involved in the swing culture to understand, but I can't imagine sharing the person I love with someone else unless I feel completely secure. So inviting another woman (or couple) to join us sexually is indicative of having a very strong commitment. Seems like weird logic to some, I know. Although we currently soft-swing, my husband and I have discussed going to the next level and I think we're both ready if the mood strikes, all individuals are attracted and in agreement, the stars align (LOL), etc. I love the idea of being able to watch my husband have sex with another woman in part because I'll be able to see everything from a different angle and (hopefully) up close. I would certainly be imagining myself in her place and would get off by knowing exactly how good it feels.
On the other hand, I was very into BDSM for several years and the sub in me greatly enjoys the idea of being made to watch my husband have sex with another woman while I'm unable to join in. Maybe being "allowed" to pleasure myself at the same time, but maybe not. Maybe being told how great it is but not allowed to participate. This particular fantasy has been in my "frequent play" list for a while now and I like it a lot, but I'm not sure I'd actually want to do it in real life. I'd have to think about that. Although there is a D/s aspect to it, I don't feel like there's quite the humiliation factor involved as there is in the usual male cuckhold situation.
It's too bad there aren't enough of us to warrant any such porn, although in the early 80's (I think), I remember seeing a video that involved a woman being tied to a chair in a bedroom and made to watch her lover have sex with another woman on the bed just a few feet away. I still think about that scene sometimes. :biggrin1: