Q. My ex and I have been separated for 6 months. Yesterday my ex refused to drop our kids off at my home because my girlfriend’s car was in the driveway. I think she thinks my girlfriend and I were seeing each other prior to our breakup, but we were not. She was a co-worker. We are moving in together very soon. When my ex got home, she texted me that she was taking me back to court to have our court order changed because she refuses to drop the kids off “under the circumstances.” I have no idea why my ex is acting in such an irrational manner. What’s good ex-etiquette?

A. Well, let’s employ Good Ex-Etiquette for Parents Rule No. 7, “Use empathy when problem solving,” to see if we can figure out why your co-parent is acting so “irrational.” This rule asks you to put yourself in your co-parent’s shoes. Here’s an educated guess.

Even though you deny that you were having an affair prior to your breakup, you said your co-parent believes you were. You did not mention the reason you feel you broke up, yet a short time after your breakup you are moving in with your co-worker. You may not have slept together prior, but if your ex is like most, she’s probably resentful that you let your interest in someone else blossom into something so strong that she believes it prompted a breakup.

So even though you did not consummate the relationship, your ex doesn’t care. Emotional affairs are still affairs. As a result, she probably feels betrayed, and seeing your girlfriend’s car in the driveway was a trigger for how rejected she feels.

What I find surprising is why you have no idea why your ex is acting this way. If you put yourself in her shoes and imagine how you might feel under the same circumstances, you will get your answer.

So, here’s more good ex-etiquette help. No one is “putting the children first.” (Good Ex-Etiquette for Parents Rule No. 1.) Not you, by moving in with someone else so quickly, and not mom for not looking for what is the easiest way to exchange the kids.

Dr. Jann Blackstone is a child custody mediator and the author of “The Bonus Family Handbook: The Definitive Guide to Co-parenting and Creating Stronger Families.”/ Tribune News Service