Hi KIP,
I would tell him his cards etc are there when he wants them, and wish him happy birthday. Them let him go and see what hissed is really like. The more he sees his dad, the quicker he will learn. He is older, you you needn’t worry- he is old enough to learn this lesson alone.
Your uncontrolling nature will be a welcome change for him, when he tires of his dad’s manipulations.
I read once that abusers are captivating at first but nauseating eventually. Your ex’s personality will begin to grate on your son soon, if it hasn’t already.