Different, but... I haven't had any contact with my dad since I was 12 years old (almost 10 years now). To me he is dead, and I will never have anything to do with him again. About the same time, my real father figure was diagnosed with cancer. I felt like you feel now, and I know it's not a nice feeling. Trust me, there is no point thinking so far into the future. In the years from now that you get to share with him, you will have many good times that will mean a lot to both of you. You should take each day as it comes, enjoy life with your father, and do your best to make sure he is happy, and also keep him on track with his diet and treatment. Best wishes, enjoy life.