On the outside, everything seems OK. You have great family days out. The children are doing well at school. Beyond occasionally snapping at each other, you don't argue and would probably describe each other as 'best friends'. However on the inside, your relationship looks very different.

When you're alone, you don't really have much to say - beyond swapping lists of jobs to be done. You can't remember the last time you had sex together and it probably felt more like another thing to tick of your 'to-list' than something passionate and truly connected.

If you stopped and thought about it, you'd probably agree that something was wrong but you're too busy – the kids need picking up from a party – or you're hoping that some future event, like the children reaching second school, is going to magically make everything better.

Sounds familiar? Welcome to the Zombie Marriage. It looks alive and well but for one, or maybe both partners, something has died. Just like zombies in the movies, these marriages can stagger on forever but they are also incredibly vulnerable.

Sandy, 45, and Peter, 46, were childhood sweethearts and beyond briefly splitting up with each other in their late teens have always been together. They have three children aged 20, 17 and 15.

'Everything should be great,' says Sandra. 'We have a nice house, three beautiful children and we've reached the point where they don't need us so much and we should have more time for each other.

'Except Peter is always working – he had a period of being unemployed and he's terrified of it happening again – so I sort of understand. He has also been acting out of character, on our youngest daughter's case about normal teenage stuff like being disrespectful, but I put it down to stress.'

However Sandy had to reassess when Peter left his phone on the kitchen worktop and their daughter noticed a flirty text coming in and alerted her.

'Peter got all defensive. She is just a "friend" and any way she's older than him. And can't he have friends? Of course he can but why has he never mentioned her before? Do friends call each other sweetheart? When I try and raise this stuff with Peter, he fobs me off: "it's just banter", apparently.'

Interestingly, it was not Peter's text friend who sparked the couple seeking help but Sandy had a training day – for her job as a teaching assistant – and felt such a strong attraction to one of the tutor's that it was completely overwhelming. 'He suggested going for a coffee and initially I said yes. Except, I'm a very moral person and it was against everything that I stood for. So I cancelled and told Peter.'

'I was in complete shock at how close both of us had come to having an affair,' said Peter. 'We talked more that night than we have done in years.'

Fortunately, they decided to seek help rather than brush things under the carpet but lots of people don't learn the lessons and after a few weeks of trying harder everything slips back to normal:

13 signs of a Zombie Marriage

Look through the list and see how many apply to you and then read through the list again and imagine answering as your husband. Afterwards look at my guide to interpreting your responses.

1. We never do anything special just the two of us

There's plenty of family time but you never or hardly ever go out together without other couple friends. OK you'll watch TV together and have a Valentine's Day meal out but it feels more going through the motions than being truly romantic.

2. I'm bored a lot of the time

Being bored is a sure sign that you're not putting enough energy into that part of your life. If you're bored with your husband, it is probably that you've stopped being interested and imagine that you know everything about him.

3. We probably have sex about three times a year

When you do have sex it's OK but it is more likely to be functional, brief and not particularly satisfying. Sometimes one or other of you will refuse sex to punish your partner or get your own way.

4. We often talk about the state of our friends' marriages

It is always easier to see what's wrong with someone else's relationship than your own. When you become pre-occupied with your friends' marriage cracks, it's a sure sign that you're avoiding looking at something closer to home.

5. We snap at each other and get defensive but never have an argument that solves anything

You think its nicer to avoid arguments but swallowing your differences means nothing comes up to the surface – where it can be solved. From time to time, the tension leaks out with snide comments or being short with each other but you can never get to the bottom of a problem – because one or both of you deny there's anything wrong or even that you're upset.

6. Sometimes I think it would be easier if I was a single parent

You have your system for doing things; your partner gets in the way, messes things up or causes arguments. Surely, life on your own would be less stressful?

7. There is something that one of us has forgiven but cannot forget

It might have been a past affair, a large gambling debt, an argument where horrible things were said or there was pushing and shoving and despite trying to move on something is stopping you.

8. I bite my tongue because there are so many topics we'll never agree about

It might something relatively trivial (like what time your daughter has to get home) or long standing deep issues (for example he doesn't like your mother) but you've stopped bringing them up because there's no point. You just side-step each other and more and more go your own ways.

9. I find it hard to get through the weekend without thinking of a special friend

It could be a male work colleague with whom you can have a laugh or compare notes about your hopeless partners or an old boyfriend that you message on Facebook who 'really' understands you. Instead of talking to your partner, you're forging an ever closer bond with someone else.

10. I have told my partner 'I love you but I'm not in love with you'

Even if you haven't said it, you'd instinctively understand someone who has. Basically, you still 'like' your partner but the passion has drained away and that feeling of being connected has gone.

11. I'm particularly close to our son and my husband has a special bond with our daughter

When you're not getting positive male energy from your husband, you're more likely to gravitate to someone who will provide it – normally your eldest son. Meanwhile, you husband is doing the same with one of your daughters. If you don't think you are too close or tell one of your children too much, ask yourself: What would my other child or children say? Do they complain that I always take my son's side? If you can recognise your husband as falling into this trap, it is likely you're doing the same (because it's always easier to see this in someone else).

12. If I won the lottery, I'd be tempted not to tell my partner

This is a sure sign that you're dreaming of starting a fresh life away from your husband or that you feel controlled by him and a bit of 'secret' money would make things easier – either way answering yes means your relationship is in deep trouble,

13. I used to be angry with my partner but now I'm indifferent

At some point, you told yourself there is no point arguing any more and switched off completely. On the surface, everything seems better – especially to your husband who is likely to breath a sigh of relief. However, it is only a matter of time before you either ask for a divorce or cross the line into infidelity (which can be an even more painful way to end your marriage).

How to assess your score

When answering for yourself… if you agreed with three of the signs, it is cause for concern but you are not in a Zombie Marriage. Four is on the cusp and five or more has you soundly in a Zombie Marriage (but you probably knew that already).

When answering for your husband… the threshold for a zombie marriage is much lower because you'll be less aware of his unhappiness than your own, so every yes is more dangerous. If you agree to two signs, it could be just a bad phase. (However, I would still be concerned if you only having infrequent sex because men use this as main yardstick for measuring the health of their relationship. My alarm bells really start ringing when one partner is withholding sex as this is the complete opposite of being loving.) Saying yes to three statements is on the cusp and four plus is Zombie Marriage territory.

But a Zombie Marriage can be saved....

13 ways to cure a Zombie Marriage

1. Have weekends away just the two of you (without the children).

2. Adopt habits that promote more time together: eat together in the evening, find TV shows to watch together, go to bed at the same time.

3. Stop calling each other Mummy and Daddy and start flirting with each other.

4. Ask for what you want rather than expecting your partner to be a mind reader.

5. Learn that its OK to say 'no' or 'maybe' and negotiate to find a solution acceptable to both of you.

6. Touch each other more: cuddle up on the sofa while watching TV, give each other a back rub, have a bath together and wash each other's hair.

7. Deal with the small issues – rather than letting them go – as this will create confidence for tackling the medium sized and later the bigger ones.

8. Put a lock on the bedroom door, so you have somewhere to be sexual without the fear of being interrupted.

9. Keep phones and other electronic devices out of the bedroom, so it feels like a private space – rather than somewhere anybody can digitally enter.

10. When there's a problem don't just label your husband as the cause, look at your own contribution to the stalemate.

11. When your partner is talking to you put down what you're doing and give him your full attention.

12. Increase the number of complements, thank yous and smiles. It takes FIVE of these positive interactions to wipe out ONE snide comment or turned back or frown.

13. Argue more. It brings problems up to the surface and shows that you care enough to engage with your husband rather than just physically or emotionally walk away.

Andrew G Marshall is a marital therapist with 30 years experience and leads a team in private practice in London and Sussex. His classic book 'I love you but I'm not in love with you' has just been reissued as a special 10th anniversary edition by Bloomsbury, £8.99

More on prima.co.uk: 20 secrets of couples who stay together forever

This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses. You may be able to find more information about this and similar content at piano.io