He grows older.

I don't think he's failing, but then there's a loss of memory, and an almost childish obsession in regard to the marriage he has set his heart on.

Then his passion for Jack seems greater as he learns little by little that Jack is not all he might be.
Wilson, I give you my word; I believe if dad ever really sees Jack as I see him or you see him, then something dreadful will happen.

In spite of everything dad still believes in Jack.

It's beautiful and terrible.
That's one reason why I've wanted to help Jack.