You left him.
You let him know that you were abandoning your family via text.
You didn't even have the courage and respect to tell him face to face that you were leaving, that you had spent time planning your exit and had set yourself up in a new home and that you were bailing on him. Everyone in your circle knew, including your children, but you didn't have the respect to tell him, your partner, your husband. The one person who should have known first, before anyone else was brought into your plan of departure.
He thought you were out walking the dog. But you were leaving him and the life that you built with him.
And now, now that he is moving on and has found a woman who truly loves him and wants to build a life with him, you are upset. I understand the heartache first hand of seeing your former spouse with someone new, your children spending time with another woman who may be a mother figure. Believe me, I've been through the ringer on that subject. But that is no reason to throw daggers at me and fill your children's heads with negative feelings. Keep those negative feelings to yourself. Your children are amazing, and they should not be subject to your unfounded opinions of me or my child. Keep the kids out of it.
Stop posting rude comments on social media. Stop trying to manipulate your children into hating me and my child. Stop playing petty games, it only shows your instability. Go hide in the bathroom with a bottle of wine and cry, or vent to a good friend like any self-respecting woman does. Social media is not the place to air your dirty laundry.
I sincerely hope that you find happiness within yourself and move on. I know and understand your situation because I have been there. I'm not your enemy. I don't need to be your friend, but we should not be at war.