I loved your letter. I thought it was excellent, to the point and there was no blaming or shaming... just concern.
Do you have a women's center in your area? Counseling services are available free of charge in most cases. If nothing else, it adds a great deal of support.
If not, remember that you can call any domestic abuse hotline 24/7 to talk to a counselor. Here is a helpful link:
Domestic Violence - State Hotlines