Why Snape turned, Snape and Lily

[Swann, Patricia]

No: HPFGUIDX 159612

> Neri:
>> In this case Snape would have *two* motivations to "turn" - 
Lily and his life debt to James. So even assuming we will find 
in Book 7 that he was in love with Lily, how can we ever know 
for sure what was the relative importance of each of these two 
motivations in his decision? <<


PS:
Or...how about this?  Lily is actually Snape's sister or half-
sister? (Snape and Petunia look somewhat alike, after all.) He 
discovers this after Lily dies and is remorseful.