This is not directed at anyone; if you take it that way, that's your choice. I'm dealing with some heavy shit right now, I lost a loved one last week, and I just need to vent, and this is as good a place and topic as any.
Again, this isn't aimed at anyone. If you're sensitive, don't read it. If you do and get bent, well, you were warned.
I think Severus was smart enough to realize that Lily didn't love him, but they were friends, first and foremost, and he loved her. It's his love for her, regardless of how she felt about him, and his guilt over her death that drove him. How many of us here don't carry some kind of guilt or unresolved pain in our hearts over the death of someone we loved? Even years later?
I think it's funny (seriously, ha-ha funny, ironic even, but kind of sad and pathetic too) that it is that very thing about him, the fact that he never let that love die, that his love for her was so great that he was turned from the Dark Path by the very threat of danger to her, that he spent the rest of his life devoted to...