I was only five when my mother left me to live with her lover. Having my own child made the pain even harder to bear

My daughter was six weeks old. She was lying on the changing mat and as I leaned over her, she smiled for the first time.

The wave of love that washed over me was literally breathtaking, it was the strongest emotion I had ever felt in my life. I knew in that moment that I would do anything for this little being in front of me, even give my own life.

It sounds melodramatic, but it was a seismic moment – ​​this was a love that truly conquered all.

I’m sure many mothers have experienced the same tsunami of love.

It’s the way to get through the sleepless nights, through the crying, and through the moment when, faced with the endless boredom of motherhood, you realize you’re having a meaningful conversation with your washing machine.

Daisy Goodwin, 6, with her mother Jocasta Innes and half-sister Tabitha in 1967

Daisy with her youngest daughter Lydia, who is now 24

It’s the evolutionary safety net that somehow makes it all worth it. Now there’s scientific “proof” that parental feelings run deeper than any other emotion.

A university in Finland recruited 55 people aged 28 to 53 who had at least one child and were all in a “love relationship.” Twenty-seven had pets. They had MRI brain scans while being played recordings of actors reading out scenarios designed to induce feelings of love, including: “Your child runs happily toward you in a sunny meadow. You smile together and the sun’s rays flicker on their faces. You feel love for your child.”

Parttyli Rinne, a researcher at Aalto University in Espoo, Finland, who led the study, said: ‘In parental love, there was activation deep in the brain’s reward system, in the striatum area, when imagining love, and this was not seen in any other form of love.’

The other types of love tested were romantic love, friendship, love for strangers, and love for pets and nature. Some pet owners may doubt the findings, but for me it rings true. Children come first.

Of course, not every woman is struck by that thunderbolt of motherly love that means nothing comes between you and your child. Many suffer from postpartum depression that disrupts bonding, which must make the stresses of early motherhood a thousand times worse. But eventually, most of these women find that all-important connection.

Yet, as I know all too well, there are women who, while they love their children, do not put them first. My mother, author Jocasta Innes, was one of them.

She was married with two children under the age of five. She lived in a Georgian house in South London. When she went to a party in Islington, she met a man with whom she fell passionately in love.

At 26, he was six years younger, a novelist living in a bedsit. They came from different worlds. She was educated at Cambridge, married to a film producer with a busy social life.

Joe Potts, who became my stepfather, was an angry young man from Newcastle (this was the 1960s) who had published two darkly comic novels. But the attraction was intense and they began an affair.

My mother thought she had found the love of her life and decided to leave my father and move in with Joe. So far, that is understandable. Many marriages end when one of the partners falls in love with someone else – and it is still common for men to leave their wives and children for a new woman.

It is much less common for a woman to leave her husband and her children. But that is what my mother did. She later claimed that she had “no choice”, that she did not have the money to take me – then five years old – and my two-year-old brother.

She was bitter about the divorce, saying the court had discriminated against her because she was the one who left, and that my father could have afforded better lawyers.

Daisy was with her mother Jocasta, who was married with two children under the age of five, when she went to a party and met a man with whom she fell passionately in love

Jocasta (pictured with Daisy) left her husband and children for another man. She later claimed she did not have enough money to take Daisy and her brother

Daisy’s father was awarded custody of his two children and they never lived with their mother again, except for visits every other weekend and half the holidays.

When Jocasta left her husband, it came at a time when unfaithful wives were portrayed as scarlet women, while straying husbands were simply following their natural instincts

I know for a fact that all of these things were true. This was before no-fault divorces and unfaithful women were painted as scarlet women, while straying husbands were simply following their natural instincts.

My father got custody of my brother and me and after that we never lived with my mother again, except every other weekend and halfway through the holidays.

My mother’s story that “I did everything I could to get custody, but the courts were against me” was one I accepted almost without question, until the day I experienced that extraordinary moment of motherly love with my own daughter. It was a moment of intense joy, but it was also underpinned by anger.

When I realized that nothing was more important to me than my baby, I couldn’t understand why my mother would choose to leave her five-year-old and toddler behind. I know she loved us, I have pictures of her looking radiant with my brother as a baby and me as a toddler, but the love she felt for us just wasn’t as strong as the passionate love she felt for her beloved.

I remember holding my own baby and wondering why she didn’t just take us, but my mother was in love with a younger man who lived in a bedsit.

Having two young children was incompatible with their passionate relationship. Either my mother was in the grip of a physical passion that was so all-consuming that there was no room for anything else, or she did not experience the same overwhelming love for her children that I had experienced with my daughter.

It was extremely painful to realize that the mother I loved so much, did not love us enough to keep us. She made a choice and her children were not part of it.

For years I wondered if it was something about the way I was as a baby that kept her from feeling the way I did about my own baby. But I have come to realize, through much therapy, that she was the adult in the situation and I was just a baby. She was the one who decided to leave and I had nothing to do with it.

There’s a part of me, a feminist part, that believes that women have the right not to be mothers, that they don’t have to define themselves as mothers first and everything else second.

Men leave their children and start second families all the time. So I don’t want to stigmatize women like my mother. It takes courage to start over like that.

There is a French saying that goes, “the children of lovers are orphans.” A couple in an intense relationship may find it difficult to prioritize children.

And it’s hard being a mother. It must be almost impossible if you don’t feel that rush of love for your children when they’re little. It’s that extraordinary sense of joy and purpose that makes motherhood so rewarding. I know it made me realize that I wanted my child’s happiness more than my own.

Of course, non-parents can experience that just as intensely, but I think it’s hard to be a parent if you don’t feel that at all.

I am no longer angry with my mother, I just regret that she never had the chance to experience the lasting happiness that I found in my children.

Her second marriage lasted about 12 years and then she moved on to someone else, but this time she took her children (my half-sisters) with her. Maybe she learned something. Romantic love can end as suddenly as it began, but the feelings you have for your children last a lifetime.

• Daisy Goodwin’s new novel Diva is out in paperback published on September 13 by Head of Zeus