Oh, that's sad to think about...  Kudos on thinking up an original idea, I must say I've never heard the "Snape Becomes A Death Eater" story told quite like this before.  One thing, though, on this line:

“I know that, you idiot! I believe that it’s perfectly normal if a Slytherin were to fall for a Muggle-born, and hate the rest of the mudbloods.” Bellatrix gave a soft gasp of disgust and left.

It was a little hard to tell who was talking there.  I'm pretty sure it was Snape (right?) but you might want to clarify that so the reader doesn't get confused.  Also, I think that Snape's sudden hatred for Lily after he spent time writing her that poem was kind of...weird.  I dunno, but you'd think he'd know she was Muggleborn, right?  I think you should have maybe added a little more of Snape's inner conflict between liking Lily and knowing her background.  That would have added an interesting side to the story.  But, these are just the rambling of an amateur.  ^_~ Excellent job on the plot though, it was really unique.  Keep writing!

Great!  I'm glad it's finally on!

You've got an interesting concept, that Snape's love of Lily not only caused his hatred of James, but also made him become a Death Eater. 

The thing about Lily being the only Muggle-born Snape likes, he really seems to be in denial.  I think i preferred it when he didn't know.  Or did he already know that from the books?

Narcissa's always busy?  It seems like she's a Death Eater but Lucius doesn't know it.  We do know that they didn't all know who their comrades were, for security.  Or maybe this is just one of Lucius' tricks, begging Snape not to tell Lily so he can prolong the conversation and persuade him?

Cool story.