I have a stalker

he keeps on calling and sending messages. I've been sleeping with him for a month, then i wanted to go, for many reasons. But he can't get over it, he keeps on coming outside my door at night, after denying his phone calls, and it scares me. He 'accidentally' meet me often around and insists that we need to talk. I refuse, after i've accepted a few times and see where is this going.
I don't want to get the police involved, as he's been in prison in the past and i don't want to cause him further trouble.
But i've to admit i'm afraid