This week Australian Liberal senator Ian Macdonald joked that New Zealand should become Australia’s “seventh and eighth state”.

It is an idea that gets bandied around every few years, almost never seriously, at least not since New Zealand declined to join the Australian federation in 1901. But with tensions raised over Australia’s detention and deportation of hundreds of New Zealanders, the Kiwis are not laughing at the joke this time.

As a half Aussie, half Kiwi, I can tell you why the idea is ludicrous. The two countries have unique histories, singular indigenous groups, and completely individual customs and charms. It might solve the visa problems of Australia’s most famous New Zealander, Russell Crowe, but the idea is otherwise unworkable.

If you said “chur” to your barista in Melbourne after ordering a flat white, you’d be met with a quizzical look (it means cheers).

If a Sydney-sider approached an unfamiliar group in Invercargill and asked to borrow a light, the terrifying stares would have her slinking quietly away.

And in New Zealand you order a “pint”, not a “schooner”, mate.

I left Australia when I was 16 – more than a decade ago now – and moved to the frigid Southern Alps of New Zealand. I woke in the mornings to Vogels bread spread with home-made blackberry jam, tea spiced with Manuka leaves and a view of snow-covered Tititea (the Maori name for Mt Aspiring).

There was much I liked about this new land, but more I didn’t understand and couldn’t relate to. New Zealanders take years to know. They can be reserved and circumspect of outsiders, particularly those from across the Tasman.

In New Zealand, Australia is a national obsession. The competition is on, mate.

For years I have flitted between the two countries, never quite at home in either place. As soon as I step off the plane in Sydney I realise I am not glamorous enough, not competitive enough, not enough enough to fully embrace my home turf.

Australians are turbo-charged in their energy and animation. When I’m in Australia I think everyone is flirting with me, even though my friends assure me they aren’t. Perhaps the vastness of the continent makes meetings between strangers immediately intimate – oh you’re here too, I’ve found you, there’s another in this great land.

When I disembark in Dunedin, I am cold – yet immediately comforted by the low-key, rough hewn locals, wearing Kathmandu fleece, jandals (what the Aussies call thongs) with socks and black puffer jackets.

Life quietens in New Zealand, things happen more slowly, and friends, job offers, relationships – they come in their own time. You can’t make things happen in New Zealand, you have to wait for them to happen to you. If you get bored waiting, you get on a plane to Australia, or Asia, or Europe.

At the moment I am reading Tim Winton’s new memoir, Island Home. I read it in bed with rain smashing against the window, bed socks on because it’s six degrees, and a vat of “gumboot” tea on the bedside table. It makes me long for the heat of Australia. The straight desert highways, the unusual wildlife and the top end – crimson dust, a smudgy blue horizon and The Heartbreak Hotel.

But when I am in Australia, I read Janet Frame’s To the Is-Land. I read it with one hand, while the other fishes ants out of my undies and scratches at my infected mosquito bites.

Then I long for the freshness and vigour of an icy New Zealand wind. The ache in my thighs as I tramp up the Dingleburn Valley with my Heading dog. The angry, stone-coloured seas that are too cold to swim in, and the crunchy tussock that serves as a bed without fear of snakes or spiders or heat stroke.

You cannot annex New Zealand – we would rebel. You cannot claim a vibrant, idiosyncratic culture as your own. And you cannot tell Kiwis to call Australia home – we don’t know the words of your anthem, and it would be a real pain to learn them.

There is a symbiosis in the relationship between the two countries that has allowed the kinship to endure through decades of colonisation, change and growth. A close friendship – g’day mate! kia ora bro! – that allows our distinct identities and quirks to flourish. Several islands adrift in the Pacific ocean, close despite the Tasman and strong in spite of our differences.

Usually mates. But no need to be more.