Interesting story which I like very much and have read before, very well written and well characterised.
But the milk thing is distractingly weird. Even if Snape hadn't been raised in the Muggle world, as we know he was, and even if he was one of those vanishingly rare Britons who drank tea black or with lemon, he'd see other people drink tea with milk (or in some cases with condensed milk, but never cream). For him to not know what milk was would be like not knowing what bread was, or eggs - it's just not credible. In fact, if he attended a Muggle primary school, he would have been given a third of a pint of milk free every school day. Free school milk was only stopped for the over sevens in 1971, the year he started at Hogwarts.