Sheldon: Or you could, y'know, keep your cool and not fight with her, or at least not in front of the boy. It takes 2 people to argue; if you don't play her game, both you and the boy win. If you continue to fall prey to her ploys, or worse remove yourself from your son's life, both you and the boy lose, especially the boy. And then you probably become the source of a lifetime's worth of problems for the boy.
It's really a no-brainer.