Yeah, it's not a good sign that she is blaming you for her actions. We each make our own decisions. It's not your fault she cheated.

I've lived through breast cancer and know how hard treatment is. It takes it's toll on the body and the mind. I had mine 13 years ago but feel that it has affected my life even though I finished treatment and beat cancer. I believe it still has a big affect on my energy level, even though it is better. Be patient with yourself, but don't take on the guilt for her being unfaithful, that was her choice.