You've captured the bleak grayness of Eileen's existence beautifully here. Obliviated by all the trappings of monotonous Muggle life, indeed.
Severus is portrayed wonderfully; he's just such a typical teenager. He's almost a different person in this setting -- the ordinary person he isn't able to be at Hogwarts.
What happens to them is utterly horrible -- but more for Eileen than Severus, because she has so much less left to lose to begin with. But as regan_v said, what goes around comes around.
I wonder if Severus ever did forget.
(Oh, and the explanation of how the potions text wound up at Hogwarts... Bonus!)