Q. My 21-year-old son who lives with me recently broke up with his girlfriend of two years. This was not a mutual split. He has found another, moved on and his past girlfriend is very hurt. I understand his decision, but I dearly miss his former girlfriend. She was part of our family for two years and I feel like I’ve lost a child. I would like to stay in touch. My son says he doesn’t care, but I don’t want to encourage the past girlfriend on my son’s behalf. What’s good ex-etiquette?

A. Your problem is no different than what any “in-law” faces when their child breaks up with someone. You are attached, they move on for whatever reason, and you miss them.

I’m an advocate of in-laws staying in touch with their children’s past partners, but that is based on the best interest of the children produced from the relationship. When there are no children, you really have to do some soul searching.

First, you said the breakup was not mutual. Therefore, your ongoing relationship with your son’s past girlfriend may give her false hope of getting back together with your son. Your conversations will inevitably include him. She’ll know what he’s doing, follow him through social media through being friends with you, etc. That will keep him forefront in her mind and if she really does want to get over him, your presence will make that more difficult — at least for now.

Second, now that your son has moved on, you will probably want to bond with the new girlfriend, as well. By encouraging a relationship with her boyfriend’s past girlfriend, she may perceive your attachment as betrayal. To complicate the issue, your son lives with you. If you want that to continue, it’s not a good idea to alienate the girlfriend.

Good Ex-etiquette Rule No. 8 is, “Be honest and straightforward.” In this case that means don’t try to secretly maintain the old relationship while cultivating the new. One or both will find out and both may feel betrayed. That’s good ex-etiquette.

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