1. OW wont be there for the long run. Your ex isnt capable of that.
2. Your ex is not a good father. You have the privilege of a life in which you get to be basically the sole' responsible carer for you children. I would never want your ex's life. I would never want OWs life. Yours is more rewarding.
3. I think kids sometimes act out more for the parent that is there. Its because they know they can and i believe They are testing the parent that is there for them... you. They want to make sure that no matter how tough their behavior is. How much they act out that you will never leave or abandon them. I think they just need tons and tons of reassurance and love. These kids left by a parent or with a parent that does bare minimum or is just doing lip service to avoid dead beat dad title need so much from the other parent. Its such a challenge.