I see BM's behavior as abuse. She is verbally abusing him and the sex thing is also abuse. If it were me I would immediately contact a lawyer and see about getting a letter drafted that basically tells BM what steps his father is going to take in overseeing the welfare of his son. If she disagrees then the matter will be taken up in court to get her parental contact supervised and have her submit to parenting classes and counseling until a time that it is determined by the court that she can have the supervision provision lifted.
