Even though you have since interacted with many beautiful girls who act in the same way as the girl that you like, she still comes to mind because you haven’t allowed yourself to get over her.
You are still thinking about what could have been.
There may even still be a part of you that is hoping that you will see her again one day.
As long as you are still emotionally attached to these desires, it will be difficult for you to give any other girl a chance.
This emotional attachment is also why you keep thinking about her during the day at your job.
Remember that you spent a year and a half looking at this girl, thinking that she was very beautiful.
That amount of time may have caused you to become more and more emotionally attached to her, even if you didn’t believe that you were interested in her at the time.
You haven’t had this kind of experience with any of the beautiful girls who are currently giving you attention.