Ugh, Mags, that sucks. Is it that he just does not comprehend how his actions affect you? Is this a personality issue? Or is he acting out in some way as an escape from something? I don't know, but I think you need to keep talking to him and find out what is going on that he suddenly seems so distant and inconsiderate.
I think what probably hurts most (if I were in your shoes), is not so much that he wants another lover or two, but how he sprang it on you without talking about what he wanted beforehand, seeing how you felt about it, etc. Then he just goes ahead and makes plans. So, of course you don't feel special!
Do you clear it with him before you date other guys? My sense is that he is probably has the attitude of "It's all good, whatever you want to do." So, he doesn't get that you need to be treated with a lot more sensitivity than he needs.
He isn't responsible for your reaction and upset feelings, but keep talking to him, and let him know how upset you are, and how tender you feel about it. I don't think it's unreasonable to ask him to slow down a bit and/or to make sure he spends more time with you. You moved to your new home to be close to him, after all!