What a lovely, complex story. I admire the way you've shown us the fine line between the moral ambiguity of two people who long for affection and will do dubious things to attain it--and the absolute moral corruption of the adult Peter we know from the books.
I have to say, though: having watched a couple teacher-student romances go sour as the younger man grows up and moves out of the older man's shadow, I see this as a very bittersweet story, Filius' dreams of a white-cloud ending aside. It's hard to watch him justify himself in this way.