As the weather (finally!) begins to chill and the holidays draw nearer, we start to focus inward a bit more — on the hearth and the home. And when outsiders mess with our domestic structure — as nontraditional as it may be — we don't take kindly to the kibitzing.

In this modern world, the idea of the familial unit is ever evolving. But what happens when some relationships simply cannot co-exist?

Let's check in with this week's letter writer to find out.

Dear Fayza,

I have been divorced for two years, and separated for three.

My ex-husband has had nine girlfriends in those three years. The latest one is the first one that gets into the middle of our arguments.

I have told her nicely that it is none of her business. Now she still gets in the middle and talks bad about me in front of my son.

What should I do?

- So Stressed Out

Dear So Stressed,

Pardon my inability to focus on the issue at hand for a moment, but nine girlfriends in three years? Um, that's a new girlfriend every 122 days. What, does he fall in love with every female cashier, gas station attendant, and waitress he meets? Guess no one could call him conservative with the use of that "girlfriend" moniker, eh?

While I'm impressed with his track record — whereby "impressed" means "skeeved," by the way — meddlesome Girlfriend No. 9 isn't at the crux of your woes.

Your ex is.

Your former husband, not his bossy broad (who will, rest assured, be history in about four months anyway), is the one to blame here.

The only thing you and his seasonal ale have in common is him. He, as the middleman, dictates the direction of the relationship between the old and new squeeze.

And he's doing a piss-poor job in his role.

As both his ex-wife and the mother of his child, he should afford you a certain degree of respect. Even if things ended badly, the existence of your son ensures that you'll be connected for the rest of your lives. He owes it to you to help make that ongoing relationship bearable, at best.

But with a revolving door of women in his — and, by association, your son's — life, and letting No. 9 talk to and about you as if you're no better than the other eight she preceded, I'm beginning to question a lot more than his choice of bed buddies.

I've got to ask the elephant-in-the-room question here. Is your ex really fit for co-rearing your son?

The attorney in me thinks it might be worth it to revisit his visitation rights and custodial privileges. No, I'm certainly not recommending you threaten to strip him from seeing his son. That would be manipulative of you, and I forbid you from using your child as leverage. You're above cowardly tactics like that.

But all things considered, would a court of law consider your ex a good father? Would the environment to which he subjects your son be considered a healthy one?

I can't make those determinations. Neither can you. My dusty J.D. wants to use the law as a crutch when in doubt.

But even I can admit that crying courtroom shouldn't be your first resort.

Before you go that far, speak with your ex — candidly, rationally, logically. You may be divorced, but you're still on the same team — Team Our Son. You can't regulate how your ex lives his life, but you're parenting this little boy together — and you have just as much say as your ex does when it comes to what's best for the boy.

It doesn't matter who your ex shacks up with. But it does matter what he's exposing your child to. A litany of temporary stepmothers and unnecessary mommybashing? What kind of behavior is his father's example going to incite in your son in the future?

Your ex's actions will have repercussions — ones you'll both be dealing with. But you can and should handle these issues to arrive at a mutually agreeable decision — for the well-being of your son.

But until you and your ex have come to an understanding, I think it's best that there's no more direct dealing between you and No. 9. Ask your ex to leave her at home (or wherever she dwells) when he picks up or drops off your son. Don't leave messages with her when she answers his cell phone. Don't discuss her in anything but a positive light with your son.

Minimize your interactions with her as much as you can. Be polite but distant when No. 9 is unavoidable. For now, you deal with him, and him only ... and wait a few more weeks until she's replaced by a perhaps more congenial No. 10.

I'm crossing my fingers for February.

Your business is all of my business. But I won't talk badly about you in front of anyone. Send an e-mail to advice@culturemap.com, message me on Facebook or Twitter, or leave a question in the comments below. Your revolving door of bad advice ends with me.