For some reason, The Washington Times did an article about Snape. Who am I to complain?
It talks all about his all-consuming, obsessive, unrequited love for Lily, and how it was one of the main things protecting Harry all those years, and led to him dying a hated and bitter man.
While some may call it 'obsessive', I don't like to think of his love for Lily like that. I mean, they became best friends at a very young age, and she was his only friend. I don't think Snape ever truly liked anyone else. Even his Slytherin friends- He didn't really like them. It was the closest thing to friendship he could have besides Lily, because there's no way he ever told them anything personal. And with that being said, it wasn't too difficult for him to fall so deply in love with her that he could never fall out. He wasn't being 'obsessive', he was being loyal. He truly cared about her, even if he was a little selfish. I never understood the whole 'love them so much you just want them to be happy' thing, myself. But either way, even after she stopped being friends with him, he still loved her and remained loyal. Even after she married James and had a baby with them, he was still loyal.
And as for 'unrequited', I refuse to believe that Lily never had feelings for Severus. Why else would she stay friends with him for so long, even after he started getting really interested in the Dark Arts? Snape never told her how much he loved her because he was insecure, and was afraid she'd say no. Lily was probably afraid of the same thing. And I think part of Snape knew she loved him back, even if he was scared to admit it. But after he called her that word, Lily must have been too angry and humiliated to carry on. It was her pride that kept her from forgiving him. Plus, I think that at that moment, she decided he must have not loved her back. If he had only told her...
But back to the article. It also talks about the Bloody Baron and his unrequited love, but I'm not going into detail. You can read the full article here.