I will jump in and say that, yes, you are making more of it than you should. Because these are new experiences for the both of you it can be hard to lay out rules when you don't yet know what to expect, or all the possible outcomes. Some people go to clubs, play sexy and dance, and go home without any significant sex play. Other nights are different. My first point to make to you is that there is no "entitlement" to sex . In swinging and in life. You didn't get "yours", and it's a bummer, but no one promised it, either.
As for your GF playing in the bathroom, it is forgivable, even if it is disappointing to you. Often, I have found, it is the women who initiate the playing, and the men allow them to get it going, as women tend to be the choosier of a pair. It might have turned into more, and unless the woman who staked out your girlfriend directly said she wasn't interested in you, then there is a possibility she was. You can still be happy for your GF's first experience, maybe enjoy that this woman was really lusting after her, and the two of you can go to the next party with the benefit of knowing more about each other and each other's needs. I'm sure your GF didn't do it "to" you; in that moment, she was being "done". It wasn't intended to hurt you, and you are right to tell her that it did. It doesn't sound like it will keep happening, and as you both gain experience( and more understanding of each other) your rules may change with you.
