I know why (and so do you)

Why do robins sing in December?
Long before the Springtime is due?
And even though it's snowing, violets are growing
I Know Why and so do you
Why do breezes sigh ev'ry ev'ning
Whispering your name as they do?
And why have I the feeling stars are on my ceiling?
I Know Why and so do you
When you smile at me
I hear gypsy violins
When you dance with me
I'm in heaven when the music begins
I can see the sun when it's raining
Hiding ev'ry cloud from my view
And why do I see rainbows when you're in my arms?
I Know Why and so do you
I Know Why and so do you