Anxiety is a strong, uncomfortable feeling of fear. It is a normal emotional response to danger or uncertainty.
All the uncertainty that comes with change can make you feel anxious. So you may feel anxious when your parents split up, because there may be so many unknowns — like what is going to happen, where you are going to live, how you will cope with all the changes, and so on.
You might also feel like you have to take sides, or choose between one parent and the other, which could make you feel anxious.
In addition, you might be worried about your relationships in the future. You might think that because your parents have separated or divorced, the same thing will happen to you. But you can learn from your parents' mistakes. What happens in your own relationships will be up to you, not your parents!
If the anxiety is lasting a long time, or it is getting in the way of your ability to do the things you normally do, get help.