Burning alive

[Winterloc]

If this has the meaning it struck me with, I think it's an effective (definitely powerful) way to depict it. When I got to shear (sheer? Or shear as a metaphor maybe?) blinds it brought to mind the character is watching someone they care for now in another relationship. You're on the outside, hence the patio light, also. Even worse, this loved one is allowing themselves to be mistreated and you come to the realization they no longer care for you/the character (reference to a clown, and your fire no longer burns for me). And I wonder if "the fire/burning" is symbolic for not only the loved ones passion, and resultant torment, but also for their energy, or attention. They are directing it elsewhere, but the character wishes it was still focused on them. The loved ones current life is consuming them and their energy (complete suffering) so there's none left to give to you. They're so emblazoned with strife that you can't even touch them.
Some sentences didn't seem concise enough to me, there's plenty of description so it needs to be cut off somewhere. See below: 

My heart pounds and I struggle to breathe(.) 
Each second seems like an hour as I stand there (,) helpless and ashamed. 
Still I watch your burning silhouette through the shear blinds that shake as you writhe and scream. 
There's nothing I can do. 
No one to call. I very much like how you contrasted the simple/to the point (especially centrally!) with your complex descriptions elsewhere. It all expanded nicely back out from this point.
The fire has consumed you now ( ; ) and all I can do is watch in horror until you convulse and collapse in a lifeless heap. You're foreseeing their demise. Could be emotionally or even physically if an abusive relationship.
It is silent now, except for the pounding in my chest that beats in slow motion. Brought into the moment   Could be: "in slow motion it beats" to ryhme with heap(s).
The patio light shines on me like a spotlight on a circus clown. 
I creep quietly away, cold and alone, 
Maybe move this line down here? because your fire no longer burns for me. Nicely ended with concise impact. 

I'm new at this critiquing thing so I hope I didn't butcher it!   Overall I think it's nicely done! Thank you for sharing.