Originally Posted by Lemondrop
I feel like I must accept that he either 1) feels strongly for the other woman, which makes me ask, where does that leave me? or 2) gives away casually what is so deeply important to me, which makes me wonder where that leaves our relationship.
Or (3), you just experience things differently from him in this area. I think you are under no obligation to feel something other than you do feel. What makes someone basically polyamorous is that they can say and mean: "I can love/be loved by more than one person to the same extent that I can love/be loved by just one person", and/or "I can love/feel loved by someone who doesn't love only me, to the same extent that I can if s/he does love only me".
I've no way of telling this for certain, but my intuition is that some people move around in this spectrum - between monamory (I hate the word monogamy!) and polyamory - and some people are where they are on that spectrum and are not going to shift; kind of similar to sexual orientation.
It may be that you are not open to being in a polyamorous relationship out of fear, insecurity, or conditioning (or that you are not open to this particular polyamorous relationship, because of who is involved) - but it may also just be that you're a one-person person. It's not easy to tell, any more than it's easy to tell what your sexual orientation is whilst under internal/external pressure to be this or that (with moral judgements swiftly on the heels of this or that).
Take your time, and be prepared to want something different from what your partner wants - that's the nature of being you rather than them