What are the last (two) lines of George Cukor's movie "A Bill of Divorcement" (1932)?

Question

The last lines of a movie are significant in many ways, but in the case of the movie A Bill of Divorcement, I don't understand what the main actors (Katharine Hepburn, in her first movie, and John Barrymore) are saying. Especially for such cases (and given that I am not a native English speaker) I usually use English subtitles. But the ones I have found seem wrong to me, and non-English ones didn't help me (seem translations of the first). The script I have found HERE (as pdf HERE) seems to be the origin of the subtitles.

What they say is:

Whats that you're playing?
Don't you recognise it?
Its my sonata, isn't it?
I've forgotten all about it.
I love to know.
You never finished it,
I tried to myself in
all sorts of ways.
No, darling, your hands
wont go like that.
Well is.
Its the silly old thing!
Whose the silly old thing?
The end of it should be further.
Should bear it up...
reaching a climax.
Who is that lovely
father you think?
Why not? You're
not born that way?

That looks wrong anyway, but even after obvious corrections it doesn't fit what we hear.

I can link to that part of the movie because luckily it is on youtube.

I came up with this:

Whats that you're playing?
Don't you recognise it?
It's my sonata, isn't it?
I've forgotten all about it.
It's most annoying have you never to finish it
I tried to myself all sorts of ways.
No, darling, you can't do it like that.
Well, this!
You silly old thing!
Whose the silly old thing?
The end of it should be ???....
It should build... 
Build!
...Be extatic!...
Isn't that lovely father? ...Isn't it ....???...
Why not?  Weren't you born like ...???..?

But the very two last lines are not complete.

What are they saying there?

Answer 1

Just from listening to it - a cleaner copy than the youtube but still pretty old & crusty - I can get most of it, but I'm uncertain on the very last line.

It's my sonata, isn't it?
I'd forgotten all about it.
It's most annoying of you never to finish it.
I tried to myself all sorts of ways.
Oh no darling you can't do it like that.
Well this.
No, you silly old thing!
Who's a silly old thing?
The end of it should be elaborated
Should build, and build. Should be ecstatic 
Oh isn't that lovely father, isn't it gay
My love, weren't we born that way?

To be honest, the last line really sounds like he's saying "when we born that wayhi", or "not playhi" but as that makes no sense…
I ran it through Izotope RX to do a bit of further cleanup, but I can't get that last line completely intelligible & trying to lip read it isn't helping.

Answer 2

After receiving an excellent answer — which still hesitates about the last two lines —, I have tried to dig up more versions of this movie and see if indeed there is no clear version. I have found one, and now I have little doubts that the last two lines are:

Oh, isn't that lovely father, isn't it gay?

Why not? Weren't we born that way?

I have cropped that part and posted it here — as proof. :)

My conclusion is corroborated by this version, subtitled in Spanish, where the last line is "Por qué no? No nacimos así?". That seems a copy of this Spanish DVD version, oddly the only one available on Amazon France, where I reside... It looks that version is more common than this one, which I don't posses yet (which might not have subtitles anyway, in case the last line is still obscure... etc.)

I don't know Russian, so I cannot use this version with a horrendous one-male-voice-dubbing that might prove illuminating.

(As they are talking about music, the main idea might have been that the joy of music is equivalent to that of life itself. But the alluded meaning of "gay" in the last line is neither "joyful" nor "homosexual", but "crazy", as father and daughter are haunted and brought together by the common peril of hereditary madness.)