How do i get my son father to sign a passport form who haven't seen him or supported him for the last 3 years.

He might sign the required document from the passport office. If not, you would have to get a court order to get his signature.  If you cannot afford an attorney, you may be able to seek help through the resources below:   Legal Aid of Northwest Texas – Free civil legal assistance to low income residents of 114 Texas counties. Eligibility guidelines can be found on Legal Aid of Northwest Texas' website. The Fort Worth office offers clinics on a variety of legal topics including general civil matters, wills, employment matters and bankruptcy. Call 1-800-955-3959 to find out more about Legal Aid, schedule an intake appointment or reserve a spot at an upcoming clinic.