Daysleeper, thank you so much for your insight — your words seem very wise. From where I am now, it can be easy to forget that time spent in a relationship is relative; this is still (all things considered) a quite new relationship, and it makes sense that with time my bond with both M and R can/will grow. Confrontation is always scary (or, well, for me it is), but I know that talking to them more about my feelings will make me feel better, so I'm going to do my best to follow your advice.
Galagirl, thanks as well for your input. You're right, I really do need to speak up... I guess, just, see above about confrontation being scary! I don't want to make them feel guilty, bla, bla. But these are standard problems; like I said, I just need to grit my teeth and speak up. :E
I'm not bored at school; I was just seeking a good way to describe the fact that I see M and R as being out in the "real world" and in some ways as fundamentally "grown up" in a way that I am not.
But I think you're also (if I'm following you correctly) catching on to the fact that I am extremely insecure about myself, and I think have been guilty of (mentally) devaluing the role I play in this relationship. It's hard, because I simultaneously want and don't want to be needed: for my own sake, I want to feel like I'm just as vital and essential to M and R as they are to each other; however, we're all aware that my moving away for grad school (or a volunteer program that I'm applying for) could cause our relationship to end prematurely. I don't want to... oh, I don't know... destabilize them or cause their relationship with each other to suffer should I not be around any more.
So you see how that creates something of a catch-22 for me where I keep feeling like I'm not "allowed" to make my emotional wants and needs known due to the fact that I, myself, feel like I somehow need to "protect" M and R's relationship with each other from me. Ridiculous, I know, but no one said anxiety had to be logical. :/