Is it love or is it something that is just in my head?

Here is the story. I knew this girl since preschool. We have worked together on three occasions and went to high school and not to mention we are neighbors (right across the street). But I didn't like her until she dated a loser who was cheating on her in high school and I knew I could treat her better. After that, I couldn't stop thinking about her, even after leaving for college and dating other women. She knows I like her and tried to express myself to her and the only thing I can get out of her is excuses. I don't know her true feelings. I moved back home and she is currently dating someone and I'm trying to get her off my mind and move on but I can't. It even hard to "holla" at a female without thinking her. When I saw first her with her boyfriend, I got chills and sad and mad at the same time. So this is why I proposed this question. I know some weak answers aregoing to show up but try to be as serious as possible.