G.C.
I told my daughter when she was about the same age, that her father and I were getting divorced. I was honest and straight forward with her... she was very aware that things were not good between us, even though we tried to hide it as much as possible from her. And I stressed that even though we would not be living together as a family that we both still loved her and we both would always be there for her no matter what. She actually handled it quite well, she did get a little emotional for a while but has gotten much better. I also let her call her dad when she feels she wants to talk to him, and he visits with them twice a week and every other weekend.
Good luck.