If you're thinking about her all the time, you've definitely got oneitis. You've exhibited all the hallmark symptoms: you think about her all the time, you're into her but she's not returning the interest (she has a boyfriend) and you like her so much even though you're not even dating her.
Take some advice from a person who's suffered from oneitis (I still get relapses from time to time): avoid it like the plague! It is absolutely terrible! It drains you emotionally and it affects all the aspects of your life. You'll be so down because of your oneitis that it will cloud your thinking and distract you from your other pursuits.
When I had oneitis, i could concentrate on my work. I would try to read a million things into every interaction we had. In my mind this girl was practically a goddess even though I wasn't romantically involved with her.
Always remember, there is no perfect girl. There are literally thousands of girls with whom you could have positive, fulfilling relationships. You have to open your eyes and see that there are plenty of other women out there.
NEVER give your heart to a woman unless she gives her heart to you. Otherwise, it's a recipe for serious heartbreak.
I'd recommend getting away from this girl. Don't diss or anything. But stop calling her, stop hanging out with her. If you run into her, be polite and friendly but don't pursue her. In all likelihood, she doesn't see you as romantic material.
Get out there and get after other women. Once you do, you'll quickly realize how little that girl really meant to you.
