On the outside, it looks like your relationship is alive and well. You turn up at dinner parties together, you're both cheering on the kids at their sporting events and the atmosphere around the house is civil - most of the time. There are certainly no screaming rows. Sometimes you're so good at keeping up appearances that you can even convince yourself that everything is okay. However, for one or both of you, something feels dead inside.
Sound familiar? I've spent 30 years as a marital therapist helping couples. Since writing my best-selling book about falling out of love, I Love You But I'm Not In Love With You, 10 years ago, my practice has been inundated with couples who ignored the warning signs and buried their problems even deeper. In the meantime, their relationships have dropped down to a lower level of hell that I've dubbed the "zombie marriage".
A good example of this growing phenomenon is Martin, 49, and his wife, Clare, 41, who have been married for 15 years and have two sons on the cusp of becoming teenagers. Three years before arriving at my consulting room, Clare had confronted Martin with the truth that although she still loved him, she no longer felt "in love".
By this, she explained, she meant "I like you" and "we're a good team together", but "all the passion between us has gone".
Not surprisingly, Martin was deeply upset by this declaration. He tried to be more considerate, get home earlier, listen more and prioritise uncompleted jobs about the house, but things soon slipped back to what they'd been before.
"I have a very demanding job that involves lots of international travel. I devoted myself to work during the week and the children at the weekend. Although I knew nothing had been fixed, Clare and I rubbed along all right ..." Martin told me, his voice trailing away.
"Until you put two and two together and made 10," Clare chipped in.
Martin had found hundreds of texts between Clare and another man who lived near them. She claimed they were just "friends" and "nothing had happened". The other man's marriage had broken down and his wife was accusing Clare of having an affair with him.
"I don't know who to believe," said Martin, "but Clare has agreed the best outcome for everybody would be for us to repair our relationship and, therefore, she won't contact him again."
"Except I don't think our marriage can be saved," countered Clare.
So there they were, living under the same roof but in separate bedrooms, pretending to the children it was because "Dad has to get up early and it's disturbing Mum's sleep" and continuing to attend social functions together. But was Clare still seeing her lover? She certainly wasn't going to tell Martin - and he was frightened to ask.
I described the stalemate as two zombies "carrying on" but going nowhere. Martin found the term particularly useful. "When I look around there are loads of zombie marriages where people stay together for the kids or have an 'arrangement' where they are 'allowed' to see other people. Although it seems to me that it's only one half who exercises the freedom and the other seems pretty miserable," he said.
So what causes a zombie marriage? Relationships don't die overnight, and the roots in many cases are in everyday life. Martin and Clare's problems stemmed from a classic cause: conflict avoidance. At first sight, it can seem like you are protecting your marriage - because who wants rows all the time? - but it comes at a terrible cost.
It is impossible for two people to live together without disagreements - in the case of Martin and Clare, he would go around turning the heating down and nag about lights being left on. His penny-pinching drove her mad, but she said nothing, to "keep the peace". In effect, she was turning off her annoyance and anger and trying to rationalise away her resentment.
However, we cannot pick and choose those feelings we switch off and soon she had lost not just the ones that she considered "negative" but also the positive feelings, such as love and respect. Worse still, by avoiding fighting, Martin and Clare lost the chance to sort out their disagreements, too.
There are other causes of the zombie marriage: infrequent and unsatisfying sex; focusing on being such great parents that you neglect being partners; unresolved problems from the past (normally an affair) and financial issues (there is not enough money to run two houses, so you soldier on).
Maggie, 53, came to see me when she discovered her husband had been having an affair for six years. "The birth of my youngest child was traumatic, I had post-natal depression - which I wouldn't admit to or get help for at the time. I was an older mother and exhausted all the time, so sex wasn't really on my radar. By the time I did start to be interested again, he was no longer interested in me."
Her husband, David, had seen it differently: "When Maggie didn't want sex with me, did I take it personally? You bet. I tried to manage the problem with pornography because I love my kids and want the best for them, but I remember reaching the point of thinking: the next person who shows an interest in me, I will respond."
You can have a good relationship if you're in what sex therapists call a "no sex" marriage (defined as fewer than four times a year) or a "low sex" marriage (fewer than 12 times a year) if both of you are happy with the quality and quantity of lovemaking. Unfortunately, sex is a difficult topic to discuss and most people end up dropping hints (that are not recognised or simply ignored), or one of you pesters and sulks (which really puts the other one off). Rather than get help, the temptation is to keep your head down and hope things will magically get better or, like David, find your own private solution.
So what can you do if, after reading this, you conclude you may be in a zombie marriage? The good news is that whether you want to kill or cure the relationship, the beginning of the process is the same. First, you must accept that anger can be positive. It brings issues to the surface, where they can finally have a chance of being solved. Having an argument is a really intimate act and it shows your partner that you care enough to show your true feelings. You will also get a pleasant surprise - once you've both had time to calm down - because nothing feels quite so overwhelming when you can talk about it.
Next, you need to be curious rather than judgmental. Why does your partner feel this way? The three most powerful words in the English language are not "I love you" but "tell me more". In this way, you can begin to walk in your partner's shoes, and if you do him or her this kindness, he or she is more likely to return the favour.
I've also yet to find a couple for whom the problems are not six of one and half a dozen of the other. Unfortunately, most people arrive in counselling with the mentality that "one of us is wrong and it's certainly not me". So instead of putting all your energy into trying to change your partner, think about what you can do differently.
When there is a row, don't go down the same old route - just shouting louder or sulking longer - but try the complete opposite. It might not be the ultimate solution, but it will break old patterns and you'll probably get a different response from your partner. Remember, you've tried the old ways to destruction and they're not working for you.
Finally, you need to stay in the ring of pain for a bit longer - rather than closing down or walking out of the room. Slowly, a way forward will emerge.
Either you will find a new understanding and a willingness to work on the marriage or a joint decision that it's time to call it quits. Whatever happens, it is better than remaining one of the living dead.
How to tell if you're in a zombie marriage
Look at the following statements and see which you agree with.
• We have plenty of family time, but rarely do something as a couple (without other couple friends present).
• When sex does occur, it is functional, brief and not particularly satisfying.
• I feel like I am tiptoeing around a silent argument that's been going on for years, but I've no real idea how it started or what it's about.
• There is something that I can't forgive my partner for having done/I did something that my partner can't move past.
• There are times I dread my partner coming home.
• I bite my tongue all the time because there are more and more topics about which we will never be able to agree.
• I would find it hard to get through the weekend without thinking of a special friend at work or some flirty texting.
• I used to be angry with my partner but, although these days he or she can sometimes be irritating, I am largely indifferent.
• I often fantasise about starting a new life once the children are older or have left home.
If you agreed with two of the statements, there is cause for concern but you are not in a zombie marriage. Three statements is on the cusp and four or more has you soundly in zombie marriage territory (but you probably knew that before you did the test).
Nine ways to cure a zombie marriage
• Have weekends away, just the two of you (without the children).
• Adopt habits that promote more time together (eat together in the evening, choose television shows to watch together, go to bed at the same time, etc).
• Explain what you want rather than expecting your partner to be a mind reader.
• Learn that it's okay to say "no" or "maybe" and negotiate to find a solution acceptable to both of you.
• When your partner is talking to you, give him or her your attention - put down your phone or tablet.
• Deal with the small issues - rather than letting them go. This will create confidence for tackling medium-sized and bigger ones.
• Touch each other more (cuddle on the sofa while watching TV, give each other back and neck rubs, stroke your partner's arm while he or she is driving the car, etc).
• Put a lock on your bedroom door so you have somewhere private to be sexual without the fear of being interrupted.
• Increase the compliments, thank yous and smiles - it takes five of these positive interactions to wipe out one snide comment.
- Canvas, Telegraph