Proof

I'm not sure I can find the words to say
To tell you how I love you so, or why;
Of course I said them once, but since that day
How am I certain that each look or sigh
Is clear? How can I best ensure my heart
Figures in my tongue, and is translated
In every fundamental, yearning part
Into your mind, and there substantiated?
How can I know my soul is bared to you
And all I think and feel exposed and shown?
How can I hope, as I perforce must do,
I do not love you wholly but unknown?
I look down and my finger, and there shines
The proof you know the love my soul designs.