My Dad has just been diagnosed

Hi, I'm new to all this. My Dad has just been diagnosed with bowel cancer and liver secondaries. I feel like my whole world has been crushed. 
we have been tild he has months not years. He is starting an infusion on Tuesday but isn't able to have tablets as his liver has deteriorated in a week. I just don't understand it all. I feel so angry. I'm trying to be strong for my mum who is being amazing as well as my two sons who are 21 and 18. All I keep asking myself is why? Why my dad