A successful co-parenting relationship requires both adults to work together throughout the process of rearing the children. While this might work for some people, it won't work for others if one party decides to stop cooperating with the other. This is problematic and can ruin the relationship. It also puts the children in a difficult spot.
If you are dealing with an ex who is suddenly uncooperative, it can be hard to figure out what to do. There are several things that you should remember. One of the most important is that you need to continue to focus on the kids. By keeping the focus on their well-being, you might find that the issues between you and your ex aren't as serious as you first believed.
You need to figure out if your ex's uncooperative nature is violating the custody order. If there are any violations, you will need to address those because the entire parenting plan is based on both adults doing their part.
It can be difficult to deal with a co-parent who is being unreasonable. At this point, self-preservation becomes a priority. You have to be able to control your own actions. Don't let your ex take control of your emotions. Trying to control you might be the only reason they are being difficult.
There are times when it becomes obvious that co-parenting isn't going to work any longer. You may have to consider moving to a new style of parenting that requires less cooperation. This can be done by modifying the parenting plan that you have now to reflect the new method.