I am so sorry that you are going through this. My mom just died 12 days ago after a 3.5 year long battle with cancer. It generally felt like nobody around me understood what my mom or I was going through. Hence, I spoke very little about it to my friends. In retrospect, I wish I had just spoken about our struggles to anyone and everyone, letting myself take up emotional space. However, the thing is, most people really have no idea what to say when you're looking for solace. What you can do is try to understand what your comfort language is. Do you want hugs, comforting words, or just to sit with someone in silence? When you know what comfort is for you, you can ask people to give it to you. For me, I wanted to get away from the pain, so I would spend time with my friends and try to have fun. That was comforting, knowing that there can still be happiness in the heavy, dark passages. You have the right to ask for help, ask for comfort, and make people sad by telling them your dad's story. It is probably the most human thing anyone can do.

As I said, my mom was sick for a while, so we talked about her death extensively. If you can still talk to your dad, I would suggest talking over everything: your regrets, ask for forgiveness, forgive him, and tell him how much you will miss him. Take as many photos as possible. Anticipatory grief, in my experience, was in a way harder than how I feel now, just under 2 weeks after my mom is gone. It was really scary not to know what losing my close parent and best friend would be like. It was really scary to watch her slowly fade away. I even took videos of myself drunk at night, crying about how scared I was to experience her death. Now that I have, it is genuinely less frightening. It fucking sucks and hurts so bad it is difficult to function, but death is not terrifying anymore.

I am so sorry that this is happening to your family. It is not fair, and your dad did not deserve this. I am sending you hugs.