I am not sure where to start here, but I suppose anywhere is better than nowhere. Reading your descriptions of Spinner's end and Eileen's life, I realised you were describing how at least half of my family lived, and one place I lived whilst at university. Most struggle to fight that never ending bleakness and monotony, but just as many use it as a form of self abuse much like Eileen. I still crave tinned tomato soup, and well, glad piping bags are the best.
The ramifications for Snape are horrendous, but I think I want to cry the most for Eileen. I always did in canon, and nothing much has changed, except that here the backlash of her first choice into this outcome is numbing in its horror and neatness. Trying to encapsulate in words that particular joy that came from her gaining Severus only to have it obliterated by the same act removing him (and destroying him) is not really possible, nor I doubt worth it because you've already done it so beautifully in the story. So beautifully created a downfall to rival any of those of the similar generation in canon, who all through desire and a certain arrogance pulled the world down with them - Dumbledore, Voldemort, the Blacks - and Eileen, although not a world changing act, does indeed change the world.
And oh, oh, Severus.
I've spent three days now thinking about the story, its pain and silences and horrors, being unsure I should thank you or wish that I had not read it. I've come down on the side that I should thank you deeply, because it is truly stunning.