kjtom, I have been in this situation too. Like brightspark says, you are not alone. (If you search for threads I started, you will find lots of good ideas and advice from people like maryz)...
I think that more parents (especially single mums) are in this situation than we ever hear about. It's domestic violence, but even more taboo because it's your own child abusing you. :( It's a horrible, horrible, almost unbearable situation to be in. If anyone else had ever treated me the way my son did, I would never have seen them again... But because he was my child, I was forced to stay in an abusive and frightening situation, and find a way of dealing with it.
I decided that I absolutely would not tolerate violence. I told my son that I would call 999 if he was ever violent. I have done it three times in the past year or so. Last time, around Easter, I had him arrested and charged. It was an almost unbearably difficult time - he was furious with me and I could barely stand to have him in the house afterwards - but it drew a very clear line. He hasn't lost his temper since, and things are a lot better :)
And I have told him that if it ever happens again, I will throw him out.
That was my 'bottom line' - you need to find your own - things you absolutely will not tolerate. You should not have to live in fear. I think you deserve a "no violence or I'll call 999" rule too.
Good luck.