Call the National Abuse Hotline - the number is in your phone book under "government listings". Ask them where the local Shelters are and go talk to them in case your husband does go over the edge. I've been there. Don't do or say anything right now to make him angry so he won't suspect what you're doing. Also call your county clerk's office (also in the phone book government listings) and ask them if they have a department that helps abused spouses file separation/divorce/restraining orders. Most courts do have this. When you file for separation, also file a retraining order and give a copy of the restraining order to the police in any county where you might be. If the police don't have a copy of this restraining order, it's likely they won't respond as fast or at all for that matter. They definately won't enforce one if they don't have a copy. Also call legal aid (govn't listing) Don't tell your son anything or involve him in any way...he night accidentally tell your husband or be scared by your husband into telling him what you do. A good site on the internet to go to for help is "silenttears.com". It helps abused women and has many, many resources. Very important -- pack a bag of close and essentials, including money for hotel/food for both you and your son and put them in the trunk of YOUR car. If you don't have a car of your own, keep it somewhere easily accessible to only you (and not where your husband will find it). Your son is of legal age to decide who to live with. I suggest if you ever do have to leave, take him with you. If you do leave without him, your husband can claim you abandoned them.
Good luck and whatever you do, make your calls today for your own safety. Don't wait in hopes someone here will give you the magical answers. You must get help now.