... 

38. We two stood there with never a third,
  But each by each, as each knew well:
The sights we saw and the sounds we heard,
  The lights and the shades made up a spell
Till the trouble grew and stirred.

39. Oh, the little more, and how much it is!
  And the little less, and what worlds away!
How a sound shall quicken content to bliss,
  Or a breath suspend the blood's best play,
And life be a proof of this!

40. Had she willed it, still had stood the screen
  So slight, so sure, 'twixt my love and her:
I could fix her face with a guard between,
  And find her soul as when friends confer,
Friends -- lovers that might have been.

 ...