Sean and I started dating shortly after I returned to Sydney from a stint in Moscow, where women who looked like models were often paired with men who looked like potatoes. I was grateful to have found a boyfriend without glaring faults. Sean was jocular and smiled a lot. He drove a red scooter, liked Christopher Hitchens and was obsessed with gadgets.

He may have underplayed his enthusiasm for watching soccer matches in the middle of the night. And I hadn't yet learnt that video games for him were a pursuit, rather than a side interest. I also overlooked his lack of interest in having children. "I just don't get the point," he said. Unusually for me, I focused on the positive. Our relationship was fresh; I was elated when his name lit up the cracked screen of my phone.

One night, after we'd been together for about two months, Sean and I went for a drive. We were in a car park overlooking the Sydney Harbour Bridge, surrounded by vehicles with steamed-up windows. In previous, longer relationships I was never at the point where I wanted to bring up marriage, but here I was discussing the future about two seconds in. I courageously told Sean that I wanted kids and that, ultimately, this wouldn't work if he didn't.

"I'll have one," he said.

I was so tickled that Sean would change his mind for me that I never digested the enormity of his answer. But for Sean, now my husband, those words define our union. One child was his compromise. One child is all I will get.

For the first two months after Clementine was born, I was fine with this - no amount of Botox will ever fix the lines etched onto my face from the sleep I lost in those days.

But soon enough, things improved. Clem started smiling. I started to anticipate her waking up more than I looked forward to her going to sleep. She was getting bigger and no longer fell asleep on me. She was no longer milk-drunk after a feed. She had also gone up one size in clothing.

"You should either sell these or give them away," Sean said about the pile of minute onesies that was steadily growing in our study. "You aren't going to need them."

Those tiny clothes were the catalyst to many heated discussions.

"But what if I want another one?"

"We agreed we are having just one."

"You agreed, I didn't. I want two."

"What would you do if I changed my mind and decided that I wanted an open marriage?"

"I didn't know I would want two kids then."

"If you told me you wanted to have two children, I wouldn't have married you. You can't just move the goalposts."

Both of us left these conversations liking the other a little less. On days when we were less hostile I taunted Sean, who found it hard to say goodbye to Clem when he went to work.

"You see," I'd tell her, "your daddy didn't want children."

"I still don't. I want child."

I am envious of my friends who have just started having children and who are all permitted to have more. They get to decide when to surrender the clothes that their children have outgrown.

As someone who is no Pollyanna, I find myself forced to cherish every moment with Clem because she might be the last baby that I will have. If I don't enjoy my first child 100 per cent, what gives me the right to demand a second?

What makes our argument more complex is that I was the one who grew up an only child. It has shaped me the same way living in an apartment compared to living in a house may have shaped me. My childhood was quiet but not lonely. Still, after having Clem, I decided that I want her to have a noisy childhood. Unlike me, she is social - I think she would enjoy the company.

I remember Sean texting his brother when he suddenly remembered the day his aunt had served them pizza with ants on it. I rarely have such recollections and don't have anyone to validate that they actually took place.

Aside from the fact that Sean treats our conversation in the car all those years ago as a pact, and one that I'm trying to break, he also thinks being an only child is good for Clementine, as she will get all of our attention.

I am anxious that this may not be a good thing as we age, especially if Clem doesn't like us. I feel if we have two children, chances are at least one will come to my funeral.

READ MORE:

When you want another baby and your partner doesn't

When you're not done having babies

Can you 'have it all' with one child?

Won't an only be lonely?

After having Clem, I started to see a therapist. I brought up the issue of wanting the second child. She advised a couple's therapist, an idea that Sean is not, so far, open to. But she also said something that stayed with me. "One of you will have to lose."

She's right. We can't have half a baby. I can't divorce Clem's father for the potential of giving her a half-sibling.

But more importantly, I don't want to see having one child as losing. My friends and Sean's parents remind me that as he was growing up, he never wanted to get married and never wanted children. They keep saying that he will change his mind. I hope he does. He is amazing with Clementine and I know that if there is a second baby, he will never wish its existence away and he will never regret the child being born.

But if Sean doesn't change his mind, all I can hope is that I will. I don't want to be bitter. It would be a waste to spend the rest of my marriage mourning a baby that never was. Sean is confident that he has made his compromise, but it will take a lot of convincing before I feel at peace with making mine.

- Daily Life