Why is it people do that?

I've never been the type of person who had much friends. Not all could understand my weirdness. That's why I was her friend for more than three years.
I guess I knew she would leave and forget me when the school was over. Maybe feared that moment.

She was a less of a friend to me. When I stopped talking, she didn't care. I listened her though. I wanted to be next to her. I looked up to her. Unconiously I copied her way of talking, thinking, feeling. She confided to me on a regular basis and I felt happy and special when she did. I've put myself for her, to be hurt. I didn't care.

I've always felt I was doing something wrong, and our relationship was fake. She faked everything, and never really opened up to me. Manipulating me. I knew but I wanted to be close to her. You know that dependancy, when you just know whatever you do, you'll end up againwith same person? She was like drugs to me. I couldn't be real friends with anybody elce, as I am not able to open myself anymore. I feel as if they wouldn't understand, I would be rejected, ignored even if I do open up.
My words became my enemy, as none would come out. Not long after everybody started flowing away from me. Nobody really listened.

Now I feel she was sticking to me, because I was needed. She recognised I am to be manipulated. She recognised my weakness. She needed me more than I needed her. I was the only fool who stick with her for the past three years, as she said. From her mouth to my ears.

I feel like a monster now. Big, fat waste of time. I am nothing next to her. I am weak. Why am I weak?