EDIT: sorry, this is really long. I didn't mean for this to be so long!
Your post reminds me very much of my own situation, except that I am in the place of your husband! I think I can offer a bit of insight, but from the other side.
Firstly you mentioned that he's quieter and that he's finding it hard to be in a conversation about your new partner. I am in that position with my partner now as well... she will tell me little things about her and her new GF and I just don't trust myself to react positively, so I say nothing. For instance she told me that she and her new partner send just a little SMS message to each other before bed to say "hey goodnight, you!" or something equally innocuous. When I heard that I just felt hurt and jealous. I
wanted to be the person she sent little text messages to like that. So instead of reacting positively about something as small as this, I just shut up and said nothing... sort of nodded or made some little sound of acknowledgment I guess. I know that I should
be okay with it, so I'm just trying to work it out in my own mind.
I just don't know, though...could he be really upset about this and just not speaking up? I worry he will go along acting like everything is is fine until one day BLAM!--He's just done with me, no warning. But if he did that, I think it would be terribly unfair to me, and I would be uber-pissed--since I have tried my very best to give him opportunities to express fear, reservations, discomfort. I can't be responsible for addressing issues I don't know are issues, you know?
I can understand how you feel, but you need to give your husband a little bit of room. When my partner found another person I had some pretty profound personal realizations. Firstly some of my childish beliefs about romance were shattered pretty violently. I went from a feeling of being belonging to a real feeling of loneliness. Since we are still pretty new to being poly I still feel profound, profound moments of utter solitude. It is hard for somebody like me who felt that they had found the perfect safety net, and then realized that the person they have come to rely on is not (or, realistically, cannot be
) everything they need.
My counselor told me that the existentialist views loneliness as the essence of the human condition. We are born alone, we travel through life alone, we die alone. It is a fact, but it need not be a source of despair. Coming to terms with your isolation can free you in ways that are not possible when bound by the delusion of interconnectedness.
A semi-opposing school of thought comes to us from Buddhism. Here the thinking is that the ego is an illusion created by the mind, and the essence of enlightenment is to deconstruct the ego. Once this is done, one appreciates that everything is connected, the mind, the body, nature, our fellows, our ideas, everything.
I think I have gotten a bit off topic now. The reason I brought it up was that something that has helped me
tremendously to come to terms with polyamory is exploring these schools of thought and pondering my own place in the universe. I don't know if your husband is anything like me, so it's hard to say if he's be interested in these things or find appreciation for these schools of thought.
My advice for communicating with your partner is to be consistent but also patient. If talking about your new partner visibly upsets him then don't mention it as frequently, but do
talk about it. There is no way you will be able to survive this by bottling up all emotion. Let your husband adjust to the idea of polyamory before really letting the tidal wave wash over him.
Good luck! Take strength from the fact that you're challenging years of dogma and societal programming! It takes real courage to be poly, be proud and supportive of your husband.