Dealing with your ex when you have children is generally not an easy feat. When parents can behave like adults, the situation is much easier. However, this isn't the case if your ex is being uncooperative. This can make the entire situation even more difficult than it has to be.
Keeping thing civil can be a challenge when you have to make serious decisions. Since your ex may try to make this impossible, and possibly miserable, there is a good chance that you will need to figure out how to stay calm in the midst of the insanity.
Double check the custody arrangement
Your custody agreement is the backbone of what happens. You need to review it to ensure that you are complying with the terms. This also gives the opportunity to know when there is something amiss with your ex's actions. Both adults are expected to follow the rules. It should be set up so that the children's best interests are the focal point. There can be long-term consequences if this isn't followed.
Find ways to remain relaxed
You can't let an uncooperative ex dictate how you behave. Sometimes, they will try to do this as a form of control. They might even get angry if they find that they can't control you any longer. Learn how to control your emotions. This is especially important if your ex is trying to pick fights. Remember that pettiness will never be beneficial during a child custody case.
Look into less direct contact
Even though you might have wanted a co-parenting relationship, you may soon realize that it isn't going to work. Exploring other options, such as parallel parenting, that involve less direct communication may be better for the children. In these methods, you will control what happens at your house. Your ex will do the same with their home. The only communication would be when decisions span both homes. You could do this in writing so that there is a record.
If you find that your child custody arrangement isn't working, you may need to explore a modification. This enables you to change the terms of the order that aren't working any longer. Parents who get along well sometimes do this as the child grows and their needs change.