Question: My 26-year-old son has been living with his girlfriend and her three young daughters for four years, and it’s not going well with them or with me.

Their relationship is marked by arguments and terrible disagreements because she is such a drama queen.

She and I were close for three years while she went through her divorce and her child-custody battles. But after everything got settled, she began to focus on my son. One day she talked so badly about him that I told her that she should quit talking and arguing in front of her girls about my son and other adult issues. My comments offended her and her 8-year-old daughter. I was giving a get-together for my daughter when the child suddenly blew up and said, “You need to apologize to my mommy for calling her a bad mommy.”

I was completely shocked and so was everyone else, but I said, “I have no idea why your mom said that, but let us adults talk about that at another time.”

The girlfriend wouldn’t come to this gathering until I had left and now — four months later — she still won’t talk to me about it. But why? I don’t interfere in my son’s life — we text more than we talk or see each other — and yet she now does everything she can to keep him away from me. I didn’t even get to see my son on Mother’s Day, but they went to see my ex-husband on Father’s Day, even though he was never involved in my kids’ lives.

What am I to do?

Answer: It all depends on how well you can swallow your pride, and that, in turn, depends on how much your son means to you. If you’d rather be right than be with him, then you should stand your ground. But it would be better if you looked at the problem from his point of view.

The young woman he chose may be difficult, but he has stayed with her and her three children for four years. Four years. A minister never pronounced them husband and wife, but for all practical purposes they are married, and the familiar admonition still stands: “Let no man put asunder.” And no woman, either.

The more you confront your son’s partner, the more he will defend her and the more he will cut you out of his life. Is this what you really want?

If it isn’t, then you’ll have to eat crow because this woman is part of your family now, and you can’t walk away from your family the way you might walk away from a club or a team. If you do, you’ll replay this sorry episode in your mind every time you go to a graduation, a wedding, a funeral and some other small family reunion.

Enough already.

It’s time to tell this girlfriend, “I’m sorry. I was wrong. I didn’t mean the things I said. I was just defending my son, and then I got carried away. Please forgive me.” Think of your apology as your gift to your son, who needs to know that you respect him and the choices he makes, and to his girlfriend, who needs to know that you won’t complain about her mothering again or get mixed up in their problems anymore. Of course, she should know that you will defend your son if she trashes him again, just as she would defend her own children. That’s what mothers do.

Above all, let her children know that you have apologized to their mother because children seldom know everything that’s going on, and this makes them worry more than they should.

Your apology will make your family stronger and also teach your son and his girlfriend a few things. In time, this young couple may even realize that their own relationship depends on good manners, too.

Send questions about parenting to advice@margueritekelly.com.

Also at washingtonpost.com Read a transcript of a recent live Q&A hosted by Kelly at washingtonpost.com/advice , where you can also find past Family Almanac columns.