I understand how you feel, Kellie--
I am back in the States now after being in Edinburgh since 2001 (not as long as you, but long enough to develop my home there). My DF is now thinking that he would like to live State-side for a few years instead of Scotland...he's never lived abroad before, so I can not deny him that. Of course, I am very torn. I know that WA is the best bet for us, because I found a great job here, one that will do wonders for my career, and my mother is on dialysis waiting a transplant, so it's great to be here for her. Sorry...I did not mean to make this about me.
I think that it might take a while for you to re-adjust to life in Chicago (or in the States as a whole). You are now a stranger in your own home.
Think of it like a sweater...when you first put it on or take it off, the neck gets a bit stretched from the "trauma" of going over your head. Once it sits there on your body (or on the bathroom floor) for a while, the fibers begin to relax and start to return to "normal".
Moving takes adjustment. And sometimes, a sweater is never excatly the same after it's been stretched, but it sure will get "close enough" to wear out of the house. As for belonging in both places, sure. "Home is where the heart is" and you now have two homes. Maybe after 8 years in the States, you will be ready to do the UK again...and the little one may be up for seeing the home of her father...and having those same experiences.
The future can hold so many things. And sometimes, we don't know what's in store for us, but it will all be good eventually....Give it time. And know that we are all here for you to vent to, cry to, and we are here to listen....