Ok I've been there and I am kinda still there currently, here's my advice:
-Block her on aim or whatever you have, that's what I did, but now i don't even go on aim because it seems to preoccupy to many people from getting on with their life
-Catch yourself whenever you are thinking about her, I remember whenever I had a spare moment the first thing my mind would think about was that girl, and what she had done and does it show if she likes me
- Talk to other women, that'll make you better with the opposite sex and you'll be having fun so you can take your mind off of her
- Disassociate yourself with her, if you here of a place with just you and her or her and a little bit of people, steer clear of it. I know it seems bad but you need to stay away from the source
-The #1 piece of advice I can give you is: DO NOT FLIRT TO MAKE HER JEALOUS. This is what I used to do but in the end it is childish and gets nothing accomplished. You should flirt to make yourself feel good, not others feel bad.
I got a lot of tips so PM me if you want more , or to be more specific on any of them