Quick point first, the relationship you're in is a "vee" not a "triad," since you and her boyfriend are not dating each other. Think of the letter "V" with your girlfriend at the hinge, and you and her boyfriend as the two arms. The reason I point that out is that the relationship dynamics in a triad are very different from those in a vee.
The only rule about poly is honesty and communication. Beyond that, every situation is different, as you pointed out.
Now I'm the type of person who likes to give advice, solicited or not. I don't expect people to follow it, I just like to provide other points of consideration. So in your shoes, I would probably point out the challenges you see with her going on a vacation that will interfere with her work life. That's not really meddling in "their relationship" because it's about her and her life and what time she has available for a vacation - not about whom she's vacationing with or the reason that person wants to take her on a vacation.
I suggest you bring these questions and concerns to the gf and possibly her bf. You sound like an extremely considerate and well-balanced gal, so I have no doubt you'll be able to find a way to bring it up in a way that makes it clear you're just trying to do right by everybody. You can emphasize your own inexperience and your desire not to hurt anybody's feelings or step on any toes and that you're just trying to communicate openly and honestly.
One specific point I'll address: "what role I play in making sure he's getting the attention he needs" ... zero. Yup, that's right. No role. They're grown-ups. If they're going to be poly, he has to learn to speak up for his own needs and she needs to learn to balance her life between her lovers. The very fact that you're asking the question assures me that you won't "overstep your bounds."
Another way to see it, is that you have as much responsibility to make sure his needs are met as you would if you were just her buddy and not her lover. Which is still none. Now, many good friends would gently point it out if they saw their friend neglecting her partner. But what she chooses to do with that information is her own decision.
I'd also like to point out something troublesome I see about their relationship and this arrangement (see above regarding unsolicited points of consideration.)
What they have is a OPP ("One Penis Policy") meaning that she can be with other girls but not other boys. What's unique here is that he also has a "OVP," which is actually uncommon in these situations. You'd be surprised how many guys think they should be allowed to sleep with other chicks without allowing the missus to sleep with other dudes.
Obviously that works fine for you, since you do not have a penis, but it could be problematic in the long term if they continue down the poly path. What I mean is that if she's interested in girls but he's not interested in boys, then this arrangement doesn't really benefit him at all, and may lead to resentment and/or envy down the road. My guess (based solely on observations of other couples in similar situations) is that she wanted to explore being with women, and she "agreed" in "fairness" that if she could have homosexual experiences, then so could he. The problem with that is that if he has no interest in homosexual experiences, then what's in it for him?
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker
Last edited by SchrodingersCat; 01-13-2012 at 07:24 AM.