The quality of life you are giving your father you are also giving to yourself. It is wonderful to look back and realize what one did for another as they declined, or passed, and not what one didn't. There are limitations in everything and those who love you, like those you love, understand or understood this, knowing it doesn't matter compared to the reality that you love.
Give yourself time and space, be good to yourself, remember him, with thanks and love,
There are no words but Carmen McRae sanga song: The Problem with Hello is Goodbye. not much different than the Buddha's: Each meeting means a parting. Treasure this time and yourself, have found no harder responsibility than just being there for those that are/were loved by me, and just doing what could be done for them, and letting them go as they will.
with much heart, your friend.