Answer:
A dagger thrust at my own heart, dictates the way I'm swayed. Left I stand, and right I yield, to the twisting of the blade.
Round as an apple, deep as a cup, and all the kings' horses can't fill it up. What is it?
What flies without wings? What passes all things? What mends all sorrow? What brings the morrow?
What has two legs but doesn't walk?
What gets wetter as it dries?
If it’s information you seek, come and see me. If it’s pairs of letters you need, I have consecutively three. What am I?