Common Tangent.

In the radius of both our circles,
Only one have realized that each others' favourite line,
That touched our hearts, and intertwined,
Was a common tangent, striking through our normals.

The circumference of our circles grow each day,
As we grow fonder and fonder of the common grey,
But one must be white and the other black,
For none can have two queens in hand,
So I guess the circle that knows,
Have to be the circle that grows,
Not in diameter but to understand,
The πr² of each others' bank,
Of feelings and thoughts,
And long dreaded walks,
In the journey called life,
So to back off,
From the common tangent.

When will the equation of the tangent be determined?
Choose a point, on either circle, 
Before it's too late, and both the turtles,
Swim away, far far away.