There are some links to possible resources for you in this thread:
Also, there is an attorney in New York named Diana Adams, and she is poly, and an advocate for non-traditional and poly families. Maybe you can contact her for a reference of a poly-friendly attorney near you: Diana@DianaAdamsLaw.net
(more information about her can be found at DianaAdamsLaw.net
All the best to you as you go through this. I would hope that his act of physically assaulting you will count against him in this process.