I am not sure if it was jealousy or maybe it was more like what IvoryTowers describes, envy. When we first got started we met a great couple that where very experienced and they really helped us a ton over the course of about a year. We played with this couple a lot over that first year and there where difenately times when I would call a halt to play sessions because things where not "feeling" right.
Now usually this was because I was have my own issues with performance and as the other husband wasn't, Mrs Van would be having a grand ole time.
So I would call stop/time out whatever and we would all stop and talk and sometimes things would return to playing and others we would call it a night. Now I never really thought Mrs Van was ever going to leave me for this guy, so I don't think I had an jealousy thoughts like that, but I might have.
Now I have definately had envy issues and usually in the size area. It took me a long time to realize that I have more to offer a playmate than size. I guess I would be considered average, but not based on most of our playmates.
That said again, I never felt Mrs Van was leaving me for one of our better endowed playmates, but I know I had thoughts of "damn wouldn't it be nice to be him?" Then I am reminded, usually after the play session ended and Mrs Van and I are alone, why she is with me.
-Van