NO NO NO you are not "flippin stupid."
You are a mom, a mama lion, who has chosen to protect her son the best she can, against a manipulative A who chooses to use his child to push your buttons.
I don't remember how old your son is, however, in some states the age is now 12 and the rest is 14 when the child can tell the judge what 'they want' as far as visitation and/or custody.
You have been on the 'correct' track with your son, for quite a while now, and whether he says anything or not, I suspect he knows which parent is the 'sane' one and which parent is the one he can 'trust.'
I suspect your son told you what 'daddy said' because he does NO trust his father to stick to his word about Easter, and he knows that you will.
So, please, take that 4 foot big rig chain that you are beating yourself up with, and lock it back up somewhere. I see absolutely NOTHING wrong with your 'response email.' It was 'precise', 'business like', and 'to the point.'
J M H O
Love and hugs,