Well, my first response to your post is to ask whether your poly relationship is closed due to a promise you made, a fluid bond, or boundaries that you all agreed to revisit sometime in the future. Because I am not sure it would be worth it to jeopardize the good stuff you've got for a fling, especially if you gave your word to being closed. Was there any kind of provision made in the agreement made among your current poly partners for opening it up?
Being poly doesn't necessarily mean that you must take every possibility for hooking up that comes your way. I think, if you are committed to your triad (or vee?) -- especially since the current situation is so new and still "settling in" as you say -- that you would learn much more from resisting the temptation presenting itself right now and get comfortable with what you have. Enjoy the tension and excitement of possibility without giving into it. Otherwise it could turn ugly between you and your partners. You wouldn't want to throw away something that has just gotten comfortable and has potential for long-term satisfaction, just for fleeting sexual gratification. Remember sexual attraction is just a chemical reaction and may not be worth the consequences if it could damage a more substantial and reliable situation.
Now, I think it'd be different if this person wanted more than sex and you saw them as someone you really might want to continue developing a relationship with. OR if there was some understanding that casual, protected sex outside your group would be acceptable if handled in a way that would still allow everyone to feel secure in the fidelity you all have agreed to. That could warrant having a discussion about opening up your current arrangement.
Perhaps one thing you could propose is that everyone in your triad agree to discussing boundaries and how everything is going for each of you, on a periodic basis so that this kind of stuff can be talked about in a level-headed objective way and not in response to lust for someone outside of your tangle. One of the things you could discuss would be the very question you asked here - how do we handle potential desires to open up our relationship to new people? You all might come up with solutions, ranging from: developing a friendship first, having everyone meet the person, giving it a time frame before becoming intimate for all to get used to the idea, to "sure, go ahead as long as protection is used" (but then you all obviously wouldn't be closed anymore).
I mean, what if all three of you wanted to change the rules every time they met someone interesting and appealing? Would you be comfortable with your partners doing that to you? When you agreed to a closed relationship, you agreed to it for a reason, didn't you?
Last edited by nycindie; 04-18-2011 at 03:17 AM.