C, Yes, it is a very strange feeling when you are not part of the "family" scenario any longer. It's difficult to hear them talk about visiting the inlaws and there you are, home alone, while they are playing house and family. Not easy.
How not to become a bitter woman? You have to learn to forgive him for his behavior and accept him for who he is today. Remember the goods times that you shared and yes, look upon your little ones as the treasures that came out of that relationship. In time, the hurt will ease, but you will never forget what transpired. Forgiveness is the first step towards letting it go and getting on w/your life. Once you've done this, everything will become easier for you. You still haven't detached enough from his drama to allow you to look at him as just a friend now and not your h. I know, easier than it is. Time will assist w/this. Keep the focus on you and your children.
Hugs!
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.