I think you should block any way he could possibly communicate with you and avoid where he might be if possible. I realize you may not be able to completely avoid him but the first time you do see him I personally would pull him aside and tell him that its not really necessary or appropriate to continue any sort of friendship with him and you'd like to go your separate ways. Just so he knows that you are entirely off limits. Considering how much it has bothered you I think this would be a good way of protecting yourself.