Let me assure you that this was a rule decided on by both of us as was our only other rule of same-room only, and I promise you, my husband would most definitely "flip out" if I were to start kissing another man. All of our boundaries were mutually agreed upon and we ventured into this lifestyle with a lot of communication and strict adherence to the parameters we set out with.
We have had many experiences over the last couple of years that haven't involved MF kissing and have found them very satisfying. The other couples/groups haven't had any problems either.
Our rules are few but, yes, they are strict as trust is a huge factor in our relationship. Neither of us are willing to jeopardize that. In all honesty, I'm the more outgoing of the two of us and I have done the majority of the legwork, so to speak, and tend to be the instigator in most encounters.
I have to disagree with you about "testing the rules". If either of us did so, the other would be hurt, feel betrayed and find that swinging isn't the right choice for us. By discussing each encounter (each one was progressive by mutual agreement) and conducting a post-mortem on feelings and turn-ons etc.. we ended up here. Renegotiating the rules is always an option but "testing" i.e. "breaking" the rules is never appropriate in the heat of the moment. Sorry.
You're right it's a jealousy thing. Aren't all the rules in place to make things comfortable for both parties in the loving committed relationship? What other motivator could there be besides jealousy (or the avoidance of such). I know for me, and I can speak for my husband too, that I don't want someone who would always be trying to get away with a "little extra".
In rereading your post I think I, initially, misunderstood what you were trying to say. If one person made a rule restricting an activity for their
own comfort but knew the other person would be fine with it, then if they unilaterally decide to break through that barrier, it's ok. Of course. I would have to agree with you there. But if there has been an agreed upon set of rules then neither party has the right to break them without discussing it first and
mutually deciding to do so.
I don't believe that was the case here.