Thousands of betrayed wives wrote to me after I revealed my divorce. I realise now there are six sorts of affair – and one is essentially the most sickening, sleazy treachery of all: ROSIE GREEN

It’s a club no one wants membership of. The cheated on. The betrayed. The tortured souls who have been deceived by the person they thought they could trust most.

When I first wrote about my marriage breaking down and my husband leaving me after 26 years together, I braced myself for some caustic responses from those judging me for airing my dirty tangas in public.

Yet while there were some negative comments, the piece prompted a response I could never have imagined.

Thousands of women started sharing their own experiences of infidelity with me. As I read their letters, I realised that as much as it buoyed me to receive them, it also helped these women to share what had happened to them. I was often the first person they told and it helped them gain perspective, made them feel less alone.

Because that’s the thing about affairs. Often we shroud them in secrecy, push them into the dark recesses of our minds to preserve our dignity – and the status quo. We think if they are not spoken of they can’t be real, and we can keep the hurt and the shame at bay.

Only it doesn’t work like that. Because like a splinter that stays embedded in the flesh, it festers, becomes infected and, slowly, inevitably, rises to the surface, creating an open sore that’s hard to heal.

In my pre-affair life, if I imagined being cheated on, I thought I would be indignant and righteous, cutting up suits and throwing them on to the lawn. I thought I would have a strong sense of being wronged.

Instead, it invoked a crisis of confidence that shook me to my core. The mental torment of rejection was unbearable. Was I unlovable? Had I done things that meant I deserved this?

My ex, defending his actions, lay some of the blame at my door: I was too needy, too lavish.

Of course, I knew I wasn’t perfect, but my discombobulated brain couldn’t sort the fact from fiction. Was I too controlling? Had I not been supportive enough? Was I not the kind, hard-working person I thought I was?

Many of the women that wrote to me shared this existential grappling with truth. Because it turns out that when your partner has an affair they often become very angry with you and this is beyond bewildering. I’ve learnt they do this because anger is an easier emotion to feel than shame.

But though other women’s emotions were similar, their affair stories were different. Some had partners who had cheated on them with prostitutes, others with their best friends. Some had tales so gasp-inducing it made my own betrayal feel pedestrian by comparison.

Their responses inspired me to create the Life’s Rosie website, where the cheated on can access help through sharing their letters – which, five years on from my divorce, continue to arrive – reading those of others, and offering their advice to those currently in the eye of the storm. Their personal stories also feature in my book, How To Heal A Broken Heart.

This new community gave me a purpose and sense of achievement, and gave others hope and support.

They confirmed that all the clichés about how to spot your partner is having an affair are true: a newfound interest in looking – and smelling – nice; out of character behaviour; staying out late (duh); going to the gym more; spending lots of time on their phone (often when locked in the loo); veering between emotional distance and over-zealous displays of affection.

It also taught me a lot about the varying types of affair, and the different challenges and emotions they throw up.

Here, with the help of couples therapist Joanna Harrison, author of The Five Arguments All Couples (Need To) Have, I share what I’ve learned about the different kinds of infidelity…

They have an affair with a prostitute

Many, many women have written to me about their partner’s infidelity with prostitutes.

On the surface, you might think this is less hurtful than them having a ‘traditional’ affair, as it’s more transactional – that it’s just about sex, rather than love or an emotional connection – and so less likely to lead to the collapse of the family due to him leaving you for the ‘other woman’.

Yet it’s still a cataclysmic betrayal that leads you to question how you could have got them so wrong.

Plus, it causes you to question why he feels the need to look outside your relationship for sexual fulfilment – which is hurtful, even if you know your sex life is not what it once was. There are also the painful practicalities of STDs and the financial outgoings to consider.

As one woman wrote: ‘I was so sickened by it all. By the betrayal and the sleaziness of it all. I feel I really don’t know him at all. He has devalued me completely. These women are younger than his daughters.’

You’re pregnant… or have a new baby

When I think of the extreme challenge of dealing with my feelings and those of my two children post-split, I cannot imagine how hard it would have been to do so with a new baby.

And if you’re pregnant when you find out your partner has been seeing someone behind your back? Just when you crave stability, your security has been smashed. The idea of dealing with the isolation of the early baby days and a relationship ending – two seismic life shifts at once – is truly horrendous.

Yet it’s a depressingly regular occurrence, particularly when the baby isn’t your first child. ‘Affairs can happen in the turmoil of pregnancy and young children, often as an escape from the difficult realities and changed status quo,’ says Joanna Harrison.

‘For the betrayed parent, at a time of life where there might have been such hopes and ideas about the future of their family, the affair can feel incredibly crushing.

‘Plus they can feel really worried that if they make room for their own feelings of grief and eviscerating betrayal that somehow they will harm their baby.

‘It’s also hard to co-parent small children when you have no trust in your partner and this can have long-term consequences on arrangements for the children. In this situation the wider support of family and friends is crucial.’

When they cheat with your best friend

Not that it’s a competition, but I think this double betrayal is the hardest to deal with.

I have had countless heartbreaking letters from women whose once loving husbands told them they were leaving for many cruel reasons (they were too lazy, too fat, too crazy, too demanding) just as their best friend was terminating their friendship saying similarly awful things.

The cheaters do this to absolve themselves of guilt, but it messes with the innocent partner’s head, decimating their self-esteem.

The final sucker punch is if the cheaters never confess to infidelity but concoct a story of getting together a respectable time later.

Chloe told me her husband and best friend – whom she met at ante-natal classes and whose children called her aunt – were having a years-long affair but both repeatedly denied it.

She had initially noticed their increasing closeness and constant messaging, and after their denials left her feeling increasingly paranoid, she eventually had to call in a private investigator to get them to admit it.

Joanna says: ‘When this happens it delivers a particular kind of devastation because of the double deception and the humiliation of being the last to know.

‘It often drags in the children from each family, who were friends with each other, and the person who is betrayed by their partner also feels confusingly bereft that their usual go-to friend is not there for them.’

The second-time-around betrayal

Samantha wrote to me recently. Her first husband, whom she was with for 16 years, had an affair with a colleague and, despite her begging him to stay, left. A year later she met someone else and they got married and have been together 18 years.

Then, a few weeks ago, she found a message that showed he had visited a sex worker.

He wants to fix things, but she previously told him she’d never accept infidelity after her first experience of it, telling me: ‘I don’t have it in me to rebuild the trust.’

I think the fear that we will be cheated on again is one that many betrayed wives share. And that anxiety can cause unwanted behaviours – from neediness to its very opposite – which require constant vigilance and self-discipline to make sure they don’t sabotage our new relationships.

‘I’ve seen situations where being cheated on multiple times can put people off relationships for life,’ says Joanna.

‘However, sometimes it evokes curiosity that can support personal development if it prompts someone to ask searching questions, such as why does this keep happening to me? Was there something unresolved from the first relationship that’s carried through into the next? Am I choosing a certain type?’

When it ends with a shock departure

A shock departure invokes a particularly destabilising kind of mental torture.

Ellie told me: ‘My partner went away to work in January of this year and literally just never came home. I never got any kind of explanation.’ Though she suspects he left her for another woman, she’ll probably never get the truth.

Joanna says: ‘A ‘shotgun’ departure, where someone leaves with no apparent warning, means the left partner is often frozen in shock and struggling to understand, playing catch-up with a partner who is already psychologically ahead of them in mourning terms – and probably wanting to move things on practically and legally as well.

‘Exiting partners may not want to look back at the pain they have caused, and so this can create an increasing chasm which isn’t helpful if they are trying to sort out arrangements over children and money.

‘The left partner may also be grappling with trying to make sense of how they didn’t spot the fact their partner was leaving.’

I gave Ellie some advice offered to me: create your own narrative about why they left and stick with it, even if you suspect it’s not the full story. It stops the agonising mental torment of why, why, why?

Affair when YOU got together from an affair

Jane wrote to me saying she was heartbroken at her partner having an affair, and the pain ‘was something she’d never wish on anyone’. Yet, she said, she didn’t feel she was worthy of my support, as her story was ‘tainted with guilt’. Why? She’d got together with her partner when he was still married.

Another woman in a similar situation confessed she and her husband had previously called his ex a ‘psycho stalker’ when she desperately searched for the truth about their relationship. Now, she was in the same position.

These women often feel their heartbreak is ‘karma’ and that they don’t have any right to sympathy. I don’t believe that at all. I feel we are all fallible, and sometimes situations push us to do things against our moral code.

And when these women are brave enough to write to me, to expose themselves to a community that feels so traumatised by infidelity, they are showing bravery.

Their letters, full of self-reflection, help us to understand why affairs happen – which is what we all need in order to move forward.

But do such stories prove the old adage that once a cheater, always a cheater?

I admit that when I started dating again I was wary of getting into a relationship with someone I knew had been adulterous before, having already experienced that heartbreak.

Absolutely not, says Joanna. However, she says that if they are repeating patterns of behaviour, then it won’t stop unless they gain an understanding of why they act this way, and what they’re expressing.

In this case, she recommends individual therapy.

• Names of letter writers have been changed. How To Heal A Broken Heart by Rosie Green (£9.99, Orion) is out now. lifesrosie.co.uk, @lifesrosie