I know its hard to understand, but speaking as a poly woman in a functional long term poly relationship, your husband has not separated his heart, he has expanded it. That expansion means more love for you too. He gets to see how much you love him by sacrificing your comfort for his in the initial out set. If he is anything like me, he is loving you far beyond what he thought possible as he is feeling added love for someone elsewhere.
I'm glad you are reading around and checking out the links. There are many of us who have been here a long time who know what has been discussed. There are some really great threads that go into great detail and then there are great threads that just point out that we are all in the same boat and can rely on each others journeys to feel comfort in our own.
*hugs* to you, its a hard journey to start but you will find, I think, that your depth of knowledge about yourself and your relationship with your husband will be incredible. The connections that can be built are beyond what you might think is possible. I'm excited for you.