If you thought that your divorce was going to be a clean break and you would not have to deal with your ex anymore, you may want to reconsider that position if you have children. The two of you are still going to have a relationship, in all likelihood. There's just no way around it.
That relationship hinges on the fact that you are both co-parenting your kids together. You may share physical custody, meaning you have to exchange the children every week. That's a face-to-face interaction you may not be able to avoid. You also have to consider how you'll spend birthdays, holidays, summer vacations and other events.
You may also share legal custody, which means that you make those big decisions together. Where are the kids going to go to school? What doctor do you want to use? How do you feel about a religious upbringing or a lack thereof?
The relationship between you and your ex changes; that much is for sure. But it is still there, and you need to know how to handle it in a new way. Even when you feel frustrated, for instance, do not say negative things about your ex in front of the kids. Remember that you want the kids to respect both of you as parents, and that means setting an example and respecting each other. Your ex should do the same for you. It's all about putting the kids first.
Shifting to this new relationship can be challenging. It is very important that you know what rights you have, what rights your ex has, and how the two of you can still work together.