agbu, your ex is not being fair. He knows how vulnerable you are, he knows how you feel. Telling you all of that and then going back to his new woman is hardly going to help is it? You need to tell him that if he ever loved you as much as he says he did then he needs to let you go. Its like he wants his cake and eat it, new life with his new woman but still you to be there for him, as it were. Maybe he thinks he is being kind - he isn't.
I'm sorry this might sound harsh, but i think you should make him drop the children at the door, i know it will be pants for them if he puts them to bed, but in the long run it is better for them. I congratulate you on being able to have a conversation with this man, but you need to move on, and right now, deep meaningful dissection of your past at the kitchen table is as about destructive as it gets. Just tell him, it is not because you are trying to be a bitch etc, but you need to move on and that it hurts having these talks, so for now, please just pick up and leave the children. Maybe it would help to have someone with you when he drops them off.
I feel for you so much, i really do - i dont have a magic pill to make this go away for you. You ARE doing amazingly well actually.
Did you go back to the doctors to discuss meds?