You should have long ago reported this to police and pressed criminal charges yourself. You should also have sought a Restraining Order from the courts. If you haven't, do so now. If not yet injured, a restraining order is supposed to protect you, and when served upon the school, would force them to comply and take action to enforce it.
If you have actually been injured by the person, yes, you might have grounds for a lawsuit against the school as well as the criminal. You should have put your complaints and requests to the school in writing, so you could prove you put them on notice of the problem.
If serious about getting legal help in this, feel free to contact me, or contact your local Lawyer Referral Service.
