Your chemic beauty burned my muscles through.
Poise of my hands reminded me of yours.
What later purge from this deep toxin cures?
What kindness now could the old salve renew?
It is the pain, it is the pain endures.
The infection slept (custom or changes inures)
And when pain's secondary phase was due
Poise of my hands reminded me of yours.
How safe I felt, whom memory assures,
Rich that your grace safely by heart I knew.
It is the pain, it is the pain endures.
My stare drank deep beauty that still allures.
My heart pumps yet the poison draught of you.
Poise of my hands reminded me of yours.
You are still kind whom the same shape immures.
Kind and beyond adieu. We miss our cue.
At face value this can be read with the following meaning: 
 My heart still pumps the poisonous liquid of your essence. 
 The reference to the circulatory system points to the way the poem is written. The same “stuff” is pumped around over and over again. In this case, it is the poison draught that is pumped through – it is the pain, it is the pain endures. 
 
 The  poison draught  is most clearly a metaphorical toxic liquid that has made its way into the bloodstream. But a  draft  is also a piece of writing, an exercise done over and over again until there’s a final draft. It’s a manual and mental labor of revision. That kind of draft, too, could be poisonous as a metaphor for  you . 

Villanelle It is the pain...