As you said, its not fair to beat yourself up in hindsight over things you should or shouldn't have done.

He's your dad, just support and be there for him. As I said before, there are effective treatments and he has a good chance of beating this demon. At the same time, I realize how gutted you must feel about it.

Keep on doing what you do, be that rock that you need to be for your father.

Best wishes to you both.