'After a very happy decade together, I told Marc that he wasn't enough for me.' Photo / File / Getty Images

Ten years into a seemingly happy marriage, Anita Cassidy, 40, told her husband Marc, 46, she found monogamy stifling and wanted other sexual and emotional partners. He agreed they could both take other lovers. But is there ever room in a marriage for more than two? The Daily Mail asked Anita, Marc and her Italian boyfriend Andrea, 30, to explain their unusual situation.

The Wife - Anita's story

About a year ago, I went public with my new relationship by posting a photograph on Facebook of Marc, my husband and I enjoying a day out with our two children.

Friends asked who the other man in the picture was. Well, I told them, it was Andrea — my boyfriend.

I know the revelation will have shocked those who thought Marc and I were a conventional couple, but the reality was that, three years ago, I sat him down at the kitchen table and we had the most difficult conversation of our lives.

After a very happy decade together, I told Marc that he wasn't enough for me.

Yes, we had a great life together and made a great parenting team. But I wanted more.

I didn't want to go sneaking off behind his back having affairs. But I told him the idea of having sex only with him for the next 40 years wasn't really what I wanted anymore.

It was such a hard thing to say. I cried and we both became very upset. Then, to my relief, he said: "Well, let's try it another way."

If you'd told me a few years earlier that I'd even be suggesting an open relationship to my husband, I'd have laughed. I was Mrs Conventional and, in many ways, I still am. My day revolves around school drop-off and pick-up, deciding whether to make a casserole for dinner, helping with the kids' homework and hockey practice.

But there had been this creeping sense that my life was lacking in some way. That there was something wrong — and I could never put my finger on it. I loved Marc, and our sex life was good. But I was lonely.

I'd tried making more friends. I joined a local writing group. There, I started writing about a woman having an affair and, as part of the research, I was reading a lot about infidelity and relationships.

One of the books was Rewriting The Rules, by Meg-John Barker. That was my lightbulb moment. The book is about relationships and why we feel we have to live a certain way. One chapter is about non-monogamous relationships.

It made complete sense to me — so much so that I asked Marc to read the book as a starting point for our conversation around the kitchen table.

I believe traditional relationships can be like an air lock. You meet someone and what you have is amazing, you try to lock it in. You shut all the windows and doors, trying to keep what you have to yourselves. But the air turns sour because there's no oxygen.

Opening up our marriage did wonders for our relationship at first. We communicated better and the sex was much better. It really was like opening the doors and windows again.

It's not that I was living a lie before. It's just that I didn't even know this unconventional side of me existed. I always thought I'd have a traditional marriage, like my parents, who were together until my dad died.

I was 28 when I met Marc at a singles' event. We married two years later. For life, I thought.

But, eight years later, as we sat at the kitchen table, we agreed to try a different type of relationship.

My attempts to meet and flirt with other people were all quite tentative at first. But then, I discovered there was this whole online scene for others who feel like I do — that monogamy is not all it's cracked up to be.

The online dating site I found asked lots of questions about the sort of things I liked sexually — things I hadn't even thought about before. It worked fast to match me with someone and I had a date within a week.

Dating again was nerve-racking. Marc stayed at home with the kids when I went out the first time, and we chatted about it when I got home.

It hadn't gone brilliantly, and I only saw that guy twice. Like a lot of people in that first year, he seemed to think non-monogamous meant "casual".

It is how some people like to manage this, but it's not my way.

Every time I had a date, Marc knew where I was going and with whom.

In time, I even introduced him to the people I was seeing. It never felt wrong, because it was all in the open.

People assume it is all about sex, but it isn't. Every so often, you find there is a real connection, as there was with Andrea, whom I met through a dating site two years ago.

We had lots in common — a love of sci-fi and reading — and we had thought long and hard about how relationships could work. It was six months before we spent a weekend together, but we became close very quickly. He met Marc after nine months and the kids after a year. They are 10 and 8 — too young to know the details, but I've explained what monogamy is and that I don't believe it's right for me any more.

Andrea sees other women. Am I jealous? Sometimes. I found it hard when he went away for a weekend with his other girlfriend, but that's something I have to work on.

I know other people struggled to understand our situation. I told my mother when she came on holiday with us and it was clear something was wrong between me and Marc. She was much more relaxed about it than I'd expected — ultimately, she just wants me to be happy.

People may think me selfish. But I think it would be more selfish — to myself and to my family — to keep plodding on when I wasn't happy.

When people criticise me, I wonder if it is because they are looking at their own marriages and asking questions. After all, we women spend our lives putting everyone else first and not really thinking about what we want.

Marc was always free to see other people but, after a few dates, it became clear it wasn't for him. A polyamorous relationship isn't for everyone.

We stopped sleeping together about 18 months ago, and agreed to separate, although we are still living in the same house. I will move out soon, with the kids. It's complicated. Andrea stays over occasionally and we all get along, Marc included.

Marc and I still spend Christmas together — we want to keep the bits of our relationship that work. Do I still love him? Of course I do, but it's no longer a sexual love. He will always be an important part of my life.

I'm aware what I'm doing raises eyebrows and I understand why. I'm sure I am the talk of the school gates. What makes me sad is that not one person has asked me about it. The reason I'm speaking out is because I think it's something we should talk more about. Monogamy isn't for everyone, just as polyamory isn't. Not everyone will find the solution I did — but it's the right one for me.

The Husband - Marc's story

We both knew Anita wasn't completely happy — at first, I thought she needed more "space'". Space away from the children and the demands of running the house. Space to write.

And, at first, that is what we tried to change, to give Anita more time and space. Having a non-monogamous relationship had never crossed my mind.

If Anita had had an affair behind my back, that would have been a dealbreaker. One of the things that made this whole thing manageable was that she was honest. If there had been deceit, that would have been the end.

I didn't tell my friends what was happening at first. I only explained the circumstances when we finally split. I'm afraid I was saddened by their reactions, which ranged from "you need a good lawyer" to "I'd never have allowed that".

I can't say I wasn't hurt. The ego takes a bit of a bashing, but more than anything, I think we both felt sad that things had changed.

Why did I go along with it? Well, I read up on polyamory and, intellectually, I could see it had a lot going for it. My initial reaction was "no, this is not for me", but what was the alternative?

Did I want my wife to be unhappily married? Absolutely not. If you love someone, you want them to be happy.

Anyway, I didn't know how I would adapt to having a different type of marriage. I was determined to at least try. We did keep talking, all the way through it. I didn't want to know all the details of Anita's dates, but we agreed that I would know who she was meeting and where, for safety's sake.

I do remember the first date she went on. She didn't stay out all night — she came back and we talked about it.

I don't think it had been quite what she was expecting. But I found it hard to be at home, wondering what she was up to.

Ultimately, it wasn't the sexual relationships that were difficult to bear, but the emotional ones.

In the early days, I was still convinced of our "specialness", that what we had was unique. I tried to see it as them enhancing our marriage, rather than replacing me. It got harder, though.

Anita and I have different memories of what triggered our decision to separate. She remembers me being upset when she came home from a weekend away with Andrea. For me, I knew it was over when we had a conversation about intimacy and she told me she was struggling to want to kiss me.

I thought, if she is struggling to feel the desire even to kiss me, then there is no point. It's true that I went on a few dates myself, but I don't think my heart was ever in it. Some men might leap at the chance to have other relationships with their wife's permission, but I've discovered I have a preference for monogamy.

I'd never been unfaithful in a relationship, even before Anita. I didn't want anyone else. It didn't feel right to me.

It was the right decision to separate, but I don't have any regrets about what we did. For me, it has reinforced what I already knew I wanted: a life with one person.

I do have that vision of being old and sitting on a park bench with a special someone, but it won't be Anita — and I wouldn't want it to be Anita if she doesn't want the same thing.

I do still love her, yes, but it's an adult love, not a swooning, heady sort of love. It's the sort of love that means accepting she needs a different type of life.

The Boyfriend - Andrea's story

When I met Anita, I had a girlfriend whom I loved very much, but I was in the process of exploring new avenues. I hoped my girlfriend would embrace this idea, too. I'd ended up cheating in a previous relationship and, while a fleeting sexual connection can be exciting, I hated the dishonesty.

Sadly, my girlfriend decided that a polyamorous relationship wasn't for her. Meanwhile, Anita and I hit it off straight away. We found we liked the same things. We went for a meal and talked the whole night. Then we went to a few exhibitions. It wasn't just about sex. For us, it was about romance, then sex.

I knew all about Marc and her kids. That's the joy of this sort of life — no secrets. It was a year before I met them, but they knew all about me: I was Mummy's boyfriend. Kids are wonderful, because they take things on board. They could accept that this was Daddy, and this was Mummy's boyfriend.

I still see other women. You'd think it might be tricky to start that conversation with someone you meet in a bar — "Hey, I love my girlfriend, but I date other women" — but people are surprisingly receptive. I think they are interested. Maybe they also appreciate the honesty.

Since I met Anita, I have been involved in another polyamorous relationship that lasted about a year. While we both enjoyed our openness, eventually we felt that our needs and boundaries were different, so we parted ways.

I'm 10 years younger than Anita, so I don't know how things will work out. Will I want children? Will that change my lifestyle? I don't know. I do feel that spending time with her children is great training for fatherhood and I feel privileged to be in their lives.

Long-term, all relationships can be difficult, whether they're monogamous or non-monogamous. I just know that this relationship is right for now.

This story first appeared in MailOnline. Appetite, by Anita Cassidy, is in bookshops and online