How Do I get an abusive live in boyfriend out of my house safely?

My live in boyfriend is verbally abusive, has been physically abusive, he seems very unstable mentally. He is already on medications for depression. He just got out of prison for his 3rd DWI in October of 2008 and is on parole.
My 2 sons live at home and we constantly fear our safety, I have told him several times that I want him to leave and he refuses; saying that he will burn the house down with me and my children inside it if I force him to leave.
I live on social security death benefits which I receive because of my husbands death. I have told him repeatedly we are NOT married. He say he would lie and say we are to force me to lose my social security benefits.
I own my home and everything in it. He has contributed nothing. I purchased it before he was released from prison.