My condolences, Doug. My father died in 1994 at the age of 70. It was liver cancer and he went from being pretty OK to dead in about 10 weeks. I still miss him about every day. Probably the best compliment I can pay him is that every time I'm faced with something difficult, I think "what would Dad do?". His voice still speaks to me now.
The situation I had was when he died, we found out what kind of shape my mom was in. She was in the first stages of that terrible slippery slope into dementia and Alzheimers. He had taken care of her and put up a good front. We knew things weren't quite right, but not to the extent they were. But on his death bed, he said "I don't know what you're going to do about your mother". And we found out pretty rapidly what he meant.
From that point on, it was a rear guard action of trying to keep her as independent as we could while also keeping her safe. The last 15 years of her life was spent under 24x7 care in an Alzheimers care facility. And probably the last 5 years, she ceased being a part of our lives. When she died a couple years ago, it was a blow, but it was also a relief.
About the only thing I can add to all the wise things said in this thread is give yourself time to grieve. For me, there was a big hole and it took time to adjust and get used to a new way of life. And talk about him. My wife's dad died in 2007. Her family is a long time German/Polish family and they *never* express emotions. I think they rely on me to bring up her dad every so often. Her mom cries when I do, but she also says don't stop doing that, we need to remember him.
Hang in there.