It is a known fact that no two people get divorced simultaneously, as far as their mindset is concerned. This will almost always create animosity post divorce.
What does it look like?
Stories, often lies, are spread about the other parent (and even about extended family) to friends and family - frankly, to anyone who is wiling to listen!
On you: By constantly bad-mouthing the other parent, you are keeping one foot stuck firmly in the past - the "past" being the relationship that you decided to leave by getting divorced. How can you expect a new partner to buy into a negative space? How can you be happy in your new life? Also, be careful if your new partner supports or encourages your behaviour.
On your children: Very young children will pick up on your negativity and anger without understanding it, causing a wide range of issues. Older children will understand that you are being hurtful to their other parent. Remember that your children did not get divorced, you did. They will always love their other parent unconditionally. You are hurting your children by hurting someone they love. You will only succeed in breaking down your own relationship with your children.
On your friends: No matter how close they are to you, they get bored of all the stories, negativity and anger. And often this behavior will alienate them from you. Friends also are not interested in the constant negativity and the unhappy environment.
How do I change it?
Getting over a divorce is one of the hardest things imaginable - and doing so alongside settling into your new life is even harder. Step one would be to draw a line under the old and to live in the present. Step Two would include formulating a great Parenting Plan so that your past stays under control as far as possible and boundaries can be set. Be the bigger person and manage your new life with respect. Respect your children enough to be the bigger person and show them what respect is all about by being a Respectful Parent, as hard as this might be with a disrespectful ex.