D.H.
My parents divorced when I was 10 and I will definitely say that the best thing you can do for her is let her know it IS NOT HER FAULT. Adults just make mistakes sometimes that can't be fixed. Make sure she knows you both love her and want to spend time with her. Let him see her as much as they both want. Also try to do things as a family. Even though you are not technically a family anymore, you are both still her parents. This is only the beginning for her of a life of trying to "split" her time between parents.
Try to be as understanding as you can and hopefully he will as well that she didn't ask for "divorced parents" and you both may have to swallow you pride for her sometimes.
I will keep you all in my prayers. May God bless you and your daughter.