I wish my parents hadnt done this from either side when I was a kid. My mother would say one thing my biological father another thinking he was setting the story straight in the end I was the one who suffered nightmares, temper tantrums until finally my mother was awarded sole custody and My father lost visitation. When I grew up I found my biological father. He told me one story and my mother told me another. and you know what? the court papers say a mixture of both. I believe the court records. Like I tell my mom now and my biological father when I found him. What went on between them should have stayed with them. neither one had the right to pull me into it. a child is a person not a piece of property for people to say mine, no mine, Im the better parent because your dad or your mom bla bla bla. I hated both of them for years because of this. Take it from someone who has been there telling the child what went on between his mom and you is not the right move. My suggestion is contact a lawyer, therapist for your son. They will ensure your child is not being pulled into this from either side and the therapist is trained to explain these things at a child level. If you need to say anything my suggestion is "thats grown up stuff I'll answer your questions when you are a grown up." The child understands you aren't going to lie or not answer you just want him to get older.Good luck in whatever you decide to do.