Im so sorry this is happening Jesika.
This is awful. I will never be able to understand how someone could actually use a child as a pawn to get revenge. You see it in divorces all the time. People will fight for custudy and visitation or deny custody and visitation for all the wrong reasons and only the child suffers.
I hope you and your ex are able to resolve this situation with his mother and protect your sons emotional well being in the process.