I told my ex that I had an abortion. I didn't, and want him out of my baby's and my life.?

I was in a relationship since July 07 with a man. I tried to leave him many times, but never did, as he was persistent, threatening suicide, displaying rage apologetic then rage and apologetic again. He has a history of marijuana and cocaine use, and in June 08 was in a mental institution for three weeks for "being a threat to himself and others". He has a temper, makes holes in walls, breaks windows, etc. and once beat me up, because I told him I wanted to break up. He is on antidepressants (on and off), unemployed since Feb 08, went on welfare, then sick benefits and was homeless (now living with his sister). I found out 3 weeks ago that I am almost 4 months pregnant with him. I told him, he promised to change, get a job, apartment, etc but hasn't shown any progress. I got the police involved after i got tired of his constant calls, emails, he ruined my reputation at work/family/friends and was constantly threatening to kill me. I lied to him and told him that I had an abortion so it'd be easier for him to leave me alone. If he'd know, he'd make my life hell and cause unnecessary stress problems for the baby. I am happy I have support from my family, I just need him to disappear from my life. The baby doesn't need a deadbeat rollercoaster dad that constantly talks about killing himself or someone that he feels mad at. MY QUESTION IS: If I bump into him one day, and he finds out I had the baby, what can he do, in terms of custody? Will withholding this from him affect me if he decides to take me to court for custody etc.? What can I do to protect myself and the baby from him to make sure he'll have no rights to the child? What can I do now to be able to prove to the courts that I am a fit mother for the child in terms of living conditions etc? Also, he is still occasionally emailing me and calling, but I don't want to call the cops, because if they throw him in jail, there will be a trial following. I don't want to show up in court with a belly for him to see. Any thoughts on that? Any advice would be wonderful from anyone. Thank you so much I appreciate you guys helping me out here. PS. I am 20 and he is 32.