Well, it sounds like your husband has been fairly good at forecasting his actions and expectations. Up until now, you've been ignoring this rather than dealing with it. Granted, I KNOW NRE is hard to handle. However, there are certain things you can do to make this easier on yourself. Ideally, you should make a point to develop a friendship with this new woman, apart from your husband. Talk to her honestly about what you are going through, go shopping together or go do something girly. This will allow you to focus more on how this new turn events can be a good thing for everybody. You will also feel more "in the loop" and emotionally secure.
I'm guessing the same is true for her.. she also wants to feel secure and a friendship with you will help that. It would be mutually beneficial. As an added bonus, it would probably make your husband really, really happy.
Anyway, that's just my 2 cents. I am good friends with my girlfriend's other boyfriend and it has been made her new relationship exceptionally easy for me to handle.