Have you tried telling him you have no interest in him whatsoever?
If you insist on doing something magical, I would suggest doing something similar to a cut ritual. Basically you anoint a taper candle with a mixture of lemon juice and mineral oil, in a counterclockwise direction from the center out to the ends. Light the candle and focus on pushing the undesired thing (person, bad habit etc) away.
Sometimes macick is not the answer. Sometimes the most powerful magick you posses is your own voice and common sense. The teen years are hard for both boys and girls... Coming of age can be a difficult thing. (I know, it sounds like parent advice!) but please give me a break, Im 41 with 5 kids! Tell him the truth! YOU DONT LIKE HIM!!!! The truth can sometimes be the most powerful macick! Dont curse someone because they have a crush on you. This is only my openion, take it as you will.