Hi

I hope I can help you a little. Early in Feb my 40 yr old daughter was diagnosed with stage Iv colon cancer with secondaries in liver. The tumours are all over the liver. 
the shock was huge for all of us. I have had some counselling and this is what I've learned about dealing with the issues. 
you have no control over the situation. You do have control over how you react. 
I had dreadful thoughts about how it might turn out, very morbid ones and I learned to push them away by saying "not now" and "stop" when they were in my head. Hard to do in the night when u can't sleep but practice helps with this and keeping yourself distracted by day. 
also like on a plane you put your oxygen mask on before helping someone else so you must look after yourself so you can be there to help yr dad. It won't help him if he thinks you look tired worried and have stopped bothering with yourself. 
do what you can to help on a practical level. Reassure him all the time that you're going to support him. 
do any and all practical things like shopping cooking washing etc. 
most important thing is one step at a time. Take each treatment or drug course a day or week at a time. Don't think ahead. Plan little treats for him and take yr lead from him. If he wants to discuss the cancer then listen and support. If he doesn't then find distractions for him. 
engage other family members or friends who can be supportive and spend time with him. 
most of all accept you have no control over this awful disease and its progress but you can try to be positive and upbeat. This will help both of you. 
try to find support groups on social media. 
my daughter is having surgery to remove the tumour as I'm writing this and will have a stoma. I knew nothing about any of this six weeks ago. It's all a steep learning curve but I'm determined to support her in the best way I can. 
good luck.