Dear Prudence: Several years ago my husband had an affair that resulted in a child. Although we're still married and he has no interest in a divorce, he lives with the child and her mother.

Our family has been shattered and my children occasionally say things that let me know they still carry a tremendous burden of hurt. But we all believe the child bears no responsibility and deserves a father.

The mother of the child, however, will never be accepted into our lives. A major problem arises around the holidays. My husband insists on coming over for Christmas, but isn't present in any meaningful sense. He just stares straight ahead.

He criticizes little things, opens gifts but never takes them with him, and refuses any offers of food. Nothing we do makes him happy and the harder we try the unhappier he seems.

I know therapy for everyone is the answer but he's never been one to open up and previous efforts have been fruitless.

What can we do to make his Christmas visit a little less awkward and perhaps even pleasant? I hate to see him so unhappy, but we're tired of having to tiptoe around him all day.

Prudence says: You all deserve a zombie-free Christmas this year. Scrooge had nothing on your husband with his thousand-yard stare, his nastiness, and his refusal to interact with his own children or take part in the holiday. I don't even understand why he comes — unless it's to make everyone glad he left.

If you are able to communicate with him, you need to have a conversation explaining that merely showing up is not enough. If he can't interact pleasantly with his family, his presence will cause more pain than his absence.

More important than Christmas, however, is addressing your oversight in not making this man your ex long ago. He has abandoned all of you, yet apparently shows up once a year to play paterfamilias, an impersonation that could better be described as paterunfamiliar.

As a gift to yourself, hire a divorce lawyer, end the marriage, and get your financial and custody issues addressed. Surely, your children would be helped by having this kind of clarity.

I agree about the benefits of therapy, but your I hope soon-to-be-ex does not have to accompany you. You and your kids all need help in sorting out the pain their father has inflicted and guidance in taking steps toward healing.

Your children need to understand his leaving, and even his strange Christmas behavior, has nothing to do with them; sadly their father is a troubled and limited man.

Once the lawyers get involved, they can help work out a visitation schedule so that your husband can establish a relationship with his children separate from you. It's likely he will take your kids to his new home. That would mean they interact with their half-sibling and her mother, which I know would be painful for you.

But for your New Year's resolution, decide to work at ending this limbo and moving on.

Please send your questions to prudence@slate.com.