The short answer is "it depends". States vary in how restrictive they are when it comes to allowing custodial parents to move; some have almost no restrictions, others view custodial move-aways with a more critical eye. If you fail to vigorously oppose your ex's plans to move, however, the court will not prevent him or her from doing so.
There are steps you can take to oppose a move-away. The following articles should get you started: