How do I protect myself from this sociopath?

I've known this man for over a year and thought I was head over heels in love with him. Three days ago somthing just clicked in my head about something he had said when we were in a huge fight the night prior so I looked it up and he is it to a t. I immediatley had a nervous breakdown since I realized how much danger I put me and my child in. I thought he was a great man and in actuality he was the most dangerous person I could have let into my life. I'm very paranoid now and he keeps coming back and I've acted a few different ways. I don't know if he's on to me knowing what I know now. I've told him many times not to come back. The last time he was here I tried not to act scared and smiled at him as if I was sad it was ending. I'm hoping I fooled him back, but I'm very scared for my saftey and my daughters. I'm so paranoid I wonder if he networked my computer, or if he made a copy of my key, or who knows what but I'm very scared. What is the best way to go about this. I'd really like advice from someone who has experienced this themselves since I feel they would be the only ones who could comprehend and understand exactly what I'm talking about and what I'm going through.