You are entitled to feel the hard things you feel, and you have the seeds of recovery in what you said, regardless of how crappy it all feels right now.
When I was diagnosed with heart issues, it hit my wife harder than me, but we both found a lot of solace in online support groups via Facebook. The people there were welcoming to family members as well as the diagnosed. Prostate cancer is much more common than my medical issue, so there are probably some terrific online support groups out there. I cannot recommend it enough. Even with HA, it let's you be proactive, let's you learn how best to help your father, and while your mileage may vary, the online support really helped me realize many have walked where you are, and many of those people have happy endings to show for it.
As an aside, I have known more than a few men with prostate cancer, but none of them passed from it.