My DF was a functioning alcoholic too, it's just so sad isn't it? 
He, too, was just so much better to be around the time he was on the wagon. I once took my young daughters to stay with him when my SM was not there. At this point he had been to a clinic and been sober for about four months. I was devastated when I saw him shiftily swig from a bottle and balance the cap on the top of the bottle rather than screwing it back on (an old 'trick' of his) so he could keep going back to it without me noticing. And I had to be there for the rest of the night as my little girls were asleep upstairs . But I was really gutted, as I had naively thought he was not a drinker any more. I felt so, so let down.
The thing is, although he was much better company when sober, (my father was a very witty, affectionate and entertaining man unless horribly plastered) he didn't believe he was better company I don't think. It was the drink which made him seemingly confident and gregarious. But then, in his later years his mother died and he never got over it. He dived headlong into bottle after bottle and it was too much, and he became bad company and a dreadful worry to his family.
On the one hand, our fathers are adults and must make their own choices about whether or not they drink when they have an addiction. On the other hand, as the people who love them, we feel we cannot stand by and just 'let' it all happen. But the thing is, your actions will neither cure him nor make him worse. Only his actions can do that.
But if you don't want him drinking in your house, then that is something you can have control over.
Feel quite emotional writing that as my DF died at 63, he was a much-loved man, but his addiction to drink ruined the last few years of his life and tarnished his relationships with his family.