There is such a thing as a prenuptial agreement done after you are married. This is called a post-nuptial agreement. But his threats that he will try to harm your immigration status are certainly of concern. There are exceptions in immigration that allow for spouses of relationships where there is domestic violence to get their immigration documents in order even with a divorce. You should contact the organization Americans for Immigrant Justice for assistance.
Vanessa Vasquez de Lara, Esq.
Attorney at Law
7700 N. Kendall Drive, Suite 412
Miami, FL 33156