Is it normal i'm still feeling this way?

This is kind of a long story, I'm sorry, but I won't include every single detail. Just the main points.

I had a very close friend named Katie. I had known her since the early nineties when I was only 3 years old. I met her because her parents were friends of my family. They met us when we first moved to the area at the time. Her and I immediately developed a friendship, and over the years we became very close. She was my best friend who was always there for me and helped me through rough times. She was better to me than anybody else, nobody made me feel as good as she did, and I was happy to know I had her in my life.
In early 2008 things started getting bad. The year had already began rough for me as it is, but come March, Katie became very sick. Doctors diagnosed her with a rare blood-related disorder known as Histiocytosis. She seemed to be pulling through over the next course of months, and although I was worried, I was confident and had faith in her recovering.
She passed away on November 26, 2008.
All efforts were, as it turned out, not good enough unfortunately. I was devastated enough that I lost my closest friend who meant everything to me and had known my whole life, but there's more to it that goes much deeper.
I have had stronger feelings for her over the years, as in wanting a relationship with her. I felt the attraction. However I wasn't sure if she felt the same way. As a matter of fact I was pretty sure she didn't. So I never said anything. After a while then I let those feelings go, and I was content that I had her as a good friend.
But I spoke with her, just a day before her passing. It was hard to see her like that, but I needed to be there for her. She talked with me for the longest time, despite how weak and in pain she was. But one thing she did tell me, gave me a feeling I'll never forget.
She told me that she had romantic feelings for me. Like the same kind I had for her. But she was too nervous to tell me before, and she didn't think I felt the same. She told me she felt that way for me ever since she first met me, and that being with me was the only thing she ever wanted in her life.

I can't even describe how I felt after that. To say that was the most horrible I've ever felt in my life...it's an understatement. I can't believe that she felt the same way as me, and I didn't even know it. I felt guilty to the point where I deserved to be in hell. She wanted me to be her lover, that's all she wanted to make her happy. But I couldn't do it because it was too late. Even though she was too nervous to tell me before, I feel I was to stupid to not notice, and too much of a coward to tell her my own feelings. Her illness may have been inevitable, but she would've have died a happier woman had things been different that way.
Following her passing, I faced about 4 months of severe depression, being sick for long periods, and anger issues. It took me almost 10 months or so to return to my normal self, but even though there were days where I enjoyed myself and was happy, I still felt horrible deep down for not being able to provide her with what she wanted most in her life.
It's been over 3 years now since she died, and I feel that I have definitely changed as a person. I've struggled with drug use for a period. At this point I think I'm just sick, as in not mentally stable. After what my mind has been through, the tragedy, the depression, the drugs..all of the damage. Now I just feel like I've gone crazy.
But no matter what state my mind is in, I still feel the same about Katie, who will always my angel. I still think about her every single day, and some days she's all I think about. From time to time I still get very sad about her, and I go somewhere I can be alone and just cry. Despite how long it's been, I still just can't live with what I've done. How oblivious and blindsided I've been..

Is it normal to still feel this way?
(Sorry for all the writing.)