I am very sorry to read of this. It is so unfortunate that so many men are walking around - like I was - with no overt symptoms of prostate cancer, of which there are exceedingly few. It sounds like he likely did not have an enlarged enough prostate that he was having troubles urinating. Sounds too, like he might have had too-few annual physical exams, or at least that included digital rectal exam and simple PSA test. This could have, and should have, been caught so much earlier.
No matter the degree and strength of your relationship with your dad, I would recommend spending as much time with him as you can. My dad lived to 99 years 10 months "with" a large cancerous prostate inside him (PSA over 200). By the time he was diagnosed, it was too late to do surgery at age 95. His doctor reasoned that he likely had prostate cancer for 15-20 years. He suffered perpetual UTI's the last five years of his life, but...I moved him from his assisted care living residence 45 miles away to a high quality similar residence 2 miles from me. I spent 5-days per week with him for 2-3 hours per day. I exercised him, ate meals with him, and we just talked about everything: life, current events, and plans for the future (he was always an optimist). I grew infinitely closer to him in those daily visits the last five years of his life, and will value those days forever. I think you will as well if you are able to arrange that...even if it might mean that he moves into your home, which I almost did with my dad.
Blessings to you and your dad...I hope God gives him longer than your description suggests that he has, but be thankful every day for what God gives him and you.