Help me

Magic isn't the right way to get revenge, because its supposed to be used for peace, not harm.
If he bullies your girlfriend, maybe you should take it up with someone at your school.

Chaosxbliss is correct on informing your school;
Yes, take it up with a school counselor. Sometimes schoold counselors will not do anything if there are not any witnesses. It would just be a battle of hear say and pointing fingers at each other. But, you and your girlfriend can legitimately report this guy. Remember United we stand, divided we fall. Also, it could get worse. At the very least, it needs to be on record as to what an a-hole that bully really is. You may even be able to file assault charges and have him go to juvenile hall. Now that, would be Karma.
I know of two bullies from two different high schools that became policemen because, they were never reported as to what kind of devious mentality they really had. No one stood up to these a-holes and reported them for future reference.
Anyway, Blessed Be.