Not really knowing him or his personality ~ or knowing you, either, it's difficult for me to be sure what to think.
Just being polite but distant could work ~ but if you feel that it won't & it isn't what you want, then maybe you do need to make it clear to him that your relationship with him is completely over ~ even as friendly aquaintances and, if you do intend to involve campus police, to give him a warning and then stop the contact completely.
You have discussed this with your mother ~ what does she think?
