Dealing from a parent's house is a bad idea to begin with but I don't think you can blame yourself entirely. If you go to school with this person, let everyone know what he did. When you see him cause a scene and make everyone around you know to stay away from the thieving narc. Life will suck hard when nobody will sell him a bag. When I was in high school I witnessed several of these little outings and it was pretty hilarious to boot.