Regarding the third, Q, originally she was on her way out. She saw how good things were when I was there, and wanted in on it, basically. She had previously checked out of the relationship, and is now working on it again, and because A & R (my significant others) love her, they're willing to let her work things out.
Q won't really talk to me about anything serious, which is why I'm of the mind that if she doesn't want to talk about it, it doesn't get to be my problem. A & R have said before that if Q gave them an ultimatum or something, they'd pick me, because I contribute more to the family emotionally, sexually, financially, intellectually, and practically. To clarify, they definitely love Q, but she's young, she doesn't have as much earning power, isn't as educated, and has a lot of emotional issues she's working out. Not the best communicator, either. So there's baggage. They love her, but life in the triad is rough, mainly because whoever isn't between the sheets at a given time feels left out, which would be somewhat resolved with the quad since they'd have someone else to go be with. There are also some financial and time resource issues happening, since Q doesn't drive. The three of them share one vehicle, and Q has to get a ride, meaning someone else's time, etc.
Also clarifying, I don't see myself as the rescuer, here. I'm not assuming it's going to be near-bliss. It will be rough at times. But I want to give it six months or so and see if we can make it work, because if we can, it will be wonderful. I think Q will likely feel better once I'm there for a while--she had this problem before I went to visit, as well, and I think she's letting her fears and worst-case scenarios percolate in her mind, making me out to be more intimidating than I am.