Everyone has already brought up very good points, not much to add that hasn’t been said. I do think you are handling it perfectly by letting Clemson know your suspicions, then letting them take the necessary action. But I just want to add that I am sorry you were violated this way. Not just on your computer, but as a second mom to this kid. I am sure you would have done anything for him or given him anything you could, but he ended up taking something from you anyway. That hurts. Sorry this happened to you. Hugs.
I do think it is important that your son understands the nefarious actions of his “best friend.” And I think you need a clear understanding of this boy’s influence on your son. A real best friend wouldn’t steal info from or impersonate his friend’s mother. Hopefully your son understands that. Best to you.