Do you have any close friends? Would you consider seeking legal assistance for his threats?
There may be some options in your area such as a temporary housing/shelter for battered women. There you would be safe from him as he would not know your whereabouts.
If you have not considered applying for social security disability for your son, that could be something to look into.
The United Way toll free # 211 dialed from a land line may direct you to a womens and children's safe location/shelter unless you feel safe at your current residence.
Another option is if you're connected with a church community, to possibly inquire about any resources/assistance they may be able to provide.
You've got to make a plan about which steps to take i.e. contact a trusted friend, phone 911 if you're fearing for your safety and that of your son, consider getting a protective order, find out which women's shelters/agencies are in your area, possibly sell items you don't need to get some additional funds, get connected to a local women's support group, if you're working and your job offers EAP benefits, you may get some free counseling, etc.
Feel free to clarify what kind of direction you're seeking.
USA National Domestic Violence Hotline at 1-800-799-7233 (SAFE)
Domestic Violence Support Organization - Online Support Group ...