Before I address your question, please note that I practice family law in Texas. I am not familar with the laws of your state. That being said, I hope I can at least give you a little help.
Sometimes in a divorce decree, there is language that states a party cannot have an unrelated person of the opposite sex spend the night when the children are in that party's possession. So obviously, if your decree has language along those lines, then you need to follow the court order.
How is your ex dictating what you do with your children during your possession periods?
Generally speaking, during your times of possession, you are the parent that makes the decisions (assuming your decree does not state otherwise). Therefore, you should be allowed to bring your children around your girlfriend.
However, if your girlfriend could expose your children to something that would negatively impact them, your ex could have grounds to ask to court to not allow her around your children.
So, as you can tell, there are a lot of details that are needed before this question can be answered. I suggest that you contact an attorney in your area. Best of luck.
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