Night and Day

[Isaias]

You are the day.
I am the night.
You are the light.
I am the dark. <<< L1-L4, very cliché. "Roses are red, violets are blue." Comes to mind
But in your sights all flames are dull,
and embers embrace a stiller soul. I enjoyed this line both in rhythm and content
You shine so bright it's hard to bare, Also cliché, feels like a filler
so I offer you my cloak to wear.
For my embrace on either side,
gives mortal eyes a place to hide. I enjoyed these last three lines. Great rhythm and imagery
The fairest face has power more
than earthly creatures can endure.
And what a pity it would find
to, by your brilliance, turn them blind.
The world of light can now be shown,
because my shadow has been thrown.
You are the day. Once again, these two lines take away from the poem
I am the night.
And by my darkness, 
light is known.

Overall a pretty solid piece, though it could definitely improve if you put a little more time into it and remain open to feedback.