This ex of yours has no sense of being committed to a woman. If you and he got remarried, he would eventually cheat on you again.

What you are doing is wasting your time on someone who will never give you what you need. Don't kid yourself with thoughts of how you are hanging with your ex for the sake of the children. You never stopped being in love with him, and that's what motivates your behavior, including calling him for advice. This will lead to nothing good for you.