erian_7 said:
Just to get the theory out--Snape became a deatheater because he loved Potter's mom and wanted the power to take her. He left the deatheaters when Voldemort killed the woman he loved, thus Dumbledore always saying love is more powerful than Dark Magic.
The problem I have with Snape's Deatheater history;
Snape heard a portion of the prophecy, thus starting Vold on the Potter Path.
somewhere in here, Snape turns to the Order of the Phoenix, feeding them information. (Per Dumbledore's testimony.)
Voldemort kills Lily, and is destroyed.
I'm not sure when they learned that Vold was going after the Potters, but I think Lily's death can't be responsibile for Snape's conversion to the Phoenix Order, given Voldemort was destroyed within moments of her death.
So, yeah, Snape may have left because of Vold killing Lily, but when Lily was killed it became a nonissue, since Vold was destroyed immediately thereafter. The prophecy is what prompted Tre-lady to be hired, she was present for 16 years in book 5. So, time-wise, it's only a couple years between the prophecy and Lily's death, at the most, probably 1 year for really knowing it was her child that the prophecy might mean. At what point Snape joined the Phoenix Order, I haven't seen, but I'm still not sure it was because of Lily.