Your love for your papa is so obviously strong just through this thread that there is no way that he didn't know how much you loved him before he left. If you can transmit that intensity of love through a computer screen to a complete stranger then your papa could feel and still can feel the love you have for him.
It's easy to look back and say what you could or should have done but it can't be undone and I think it's probably just your own harsh judgement of the time. I'm sure that your papa never once questioned how often or how long you visited him in the end.
From your message it seems like your papa was a pretty amazing man with a lot of love and warmth for his family. He shall always live on in your memories and it is your 'duty' to keep his memory alive by remembering all the good times rather than dwelling on the possibilities.
Where ever your papa is now I'm sure he's beaming down on you and your family with pride. A person that special will always leave behind a mark on another person's soul and he has very much done that with you. Nurture that mark on your sole and take from it all that you can.
I hope that this holiday time for you is as easy as it can be. Take care.