Amylynn,
Kathy mentions crying in the shower ... I got pretty good at doing it while driving during my darkest days. Have to keep your eyes open, though.
I have found that reading poetry helps me deal with emotions. The earliest poetry that we have - Chinese and Hittite poetry going back thousands of years gives voice to joy and sorrow, hope and despair. I am not a conventionally religious person, but I do not believe that love and beauty of spirit are ever wholly lost. There is love and strength to find in poems, in religious works, in the words and glances between father and daughter.
You are doing your best - all that is humanly possible to help your father fight this thing. You cannot, however much you wish, return youth and health. You can bring love and meaning and solace in the days ahead.
Maria