As much as you want to get back at him, you will probably feel like you have stooped to his level if you do and later regret it. So save yourself the extra pain of dealing with your own conscience in the future. He also probably wants you to get back at him by responding with a mean letter of your own. That way he can feel justified in continuing his poor treatment of you and he can have a "reason" to fight and a "reason" to abandon his commitment.
