The mother has sole custody. Son has changed schools to live with me. Her home is unstable she is back and forth with her husband, still talks around my son that she will leave her husband. My son has adjusted well to living here. Her own parents thought that it was best for my son to be with me. His mother threatens my son if he wants to stay with me for a weekend that she will take him back if he doesn't come to her house.

Didn't you get this changed when the son started living with you? Are you still paying child support to the mother? What is the current visitation plan that is ongoing?