How do I let this guy understand that I am NOT interested ?

ok, there is this man his daughter goes to the same school as my son, he is married!

I have known this guy in the passed. I dated him in 2005 (I was separated from my ex husband at the time) but we only dated for few months and he wasn't married. Things didn't work out and I left him and he was fine with it.

Now I see him every day in my son's school and he tried to chat me up more than once. Last week he stopped me and said that he would like to give me his number so we can chat, I told him I have a partner and I am not interested but he didn't believe me and said no you're lying!! He's in his 40s now. I have a bf and I love him to bits and would never go back to this guy, also he is married what does he want from me??

Today he was staring at me in school and I saw him following me, seriously he scared the hell out of me!!

I am NOT interested and have told him that I have a partner but he doesn't believe me. I also told my bf and he was so angry and asked me to call the cops. My bf is away at the moment otherwise he would have gone to him and prove to him that I am his gf.

This man won't leave me alone and seriously if he continue following me I would definitely call the cops but at the moment I don't want to make it big, he need to realise that I have a bf and not interested plus he is married what the hell does he want from me??? And not to be mean but I feel sick everytime I see this guy :/