Is it normal to feel this way about my ex-friend?

It's going to sound strange, but here goes.
I had a friend and we were friends for six years, we met in secondary school and were friends ever since. In year 8, I found out that she had feelings for me - my other friends couldn't keep their mouths shut so I heard it from them first, then they proceeded to make fun of me and her. At the end of the school day, she confessed to having feelings for me and I said it was okay, because it was. However, for the rest of the years at school, I constantly took it for granted and with everyone else always making fun of me and her (even though we weren't dating) I became a really horrible person. I made fun of her too, I played with her feelings and purposely hurt her, but I liked it. I liked having that sort of power, but when other people used to hurt her, I got extremely defensive of her and stood up for her. I liked seeing her happy, but only if I was the cause of her happiness. But I remember that I hated her, that she annoyed me so much and I don't know why.
Then family issues ensued with me, I entered a state of depression and long story short, she took that for granted and started manipulating me. She drilled it into my head that we were 'destined for each other' and that it was fate that we met. I started to believe her. We dated, it didn't work out, we stopped dating.
Years later, after we finished school, she dated a guy and I got jealous and angry, but I didn't know why because I was determined that I didn't feel anything apart from just casual friendly feelings for her after we dated, however I still was angry and jealous and defensive.
Then they broke up because he was violent and mean, and she and I started dating again. I was unsure in the relationship, basically frigid if you want to be blunt, and I said I couldn't do it. I did have feelings for her and I did enjoy her company, however I just felt uncomfortable when we would kiss or hug. I was self-conscious more than anything, I'd never had a proper relationship.
We broke up on mutual terms and then we were closer than ever. Then she started dating the same guy she dated before, but he claimed that he had changed. He hates me, just saying.
Anyway, me and her had this huge falling out because of it and I went crawling back to her, apologising for everything, and I meant everything - from the past to the present, I meant it. She said she couldn't go down that path again with me and she stopped talking to me. Before, I was angry because she was dating /him/ again, but now? I honestly don't care, I just want her in my life.
I felt utterly broken - empty. My entire body shook and I cried for three hours straight. I knew she had every right to hate me; she blamed me for her depression (which was uncalled for considering I'm the one that helped her out of the depression that her boyfriend put her in), she's always on my mind and it hurts to think about her. I feel lost and scared; I've never felt this way about anyone before; after years of going through everything with her and not having her here, I don't know what to do. I think about her and I just want to die - quite literally. I think I'm obsessed with her.
So, am I in love with her? Or am I just a sick, twisted menace? Is this normal?