Have you filed for divorce yet.? You did not mention your son’s age. Setting up custody is important. My daughter is a lawyer and has been assigned to represent the children not either parent with regards to custody. Your estranged husband can not alienate you from your son. Obtain professional help as quickly as you can. The longer this goes on the more damage to you and your son’s relationship. Keep trying to communicate with your son. Don’t make him feel he must choose sides. Just let him know you love him unconditionally. Best of luck to you