“Carl has joked about going out to sea on his boat. Put in so much fuel and just go in one direction. And, you know, the fuel’s going to run out eventually …”

Kiko Matthews is not one to duck a subject. She lives with Carl Hayman, the former All Black prop, and their infant daughter in New Plymouth, where they run a boat-charter business. She is also living with Hayman’s recent diagnosis of dementia. Time is something other people have; talking around a subject likewise a luxury alien to her.

“Carl will say,” she recounts matter-of-factly “and I totally get where he’s coming from: ‘What’s the point in living? It’s only going to get worse. I’ve got headaches every day. I can’t function. And this is as good as it’s going to get.’ There is no cure.”

Related: Rugby’s dementia stand-off: ‘They ignore it. It’s just deny until you die’

Matthews, at 41, is 18 months Hayman’s junior and a survivor of a life-threatening illness herself. In 2009, she was diagnosed with a tumour on her pituitary gland, which causes Cushing’s Disease, and again in 2017. Each time, she underwent neurosurgery to remove it. A few months after her second brush with mortality, she broke the world record for rowing solo across the Atlantic. A year later again, she was cycling around the coast of the UK and part of Ireland, organising impromptu beach clean-ups and raising awareness of single-use plastics.

While training for the latter, she met Hayman in March 2019 when they joined a peloton cycling the length of Britain for Doddie Weir’s foundation. Hayman was going through a divorce and was about to leave his job as forwards’ coach at Pau, having been convicted for domestic violence. He returned to France, but they continued their relationship remotely as she completed her bike ride.

She noticed he seemed to drink a lot on his own and went through dark moods, what he called his “man periods”, but when they were together all seemed well – bar Hayman’s terrible headaches. “You’ve probably got a sore head because you’ve had it bashed in so many times. You’re up and down because you’re going through a divorce. That was our thinking then. Actually, as it turns out, that divorce was probably related to the CTE [chronic traumatic encephalopathy], rather than the other way round.”

The man himself is in agreement. The diagnosis has at least identified the problem and allowed them to plan for it. “A few years ago, I was just not well at all,” Hayman says. “I didn’t understand what was going on with me.”

Fast forward another two years, and they had moved to New Zealand together and had a daughter, Hayman’s fourth child. But the headaches and depression only seemed to deepen. On the advice of the Wales international Alix Popham, who has been diagnosed with dementia, they returned to England for testing at King’s College London, which is when, in July 2021, Hayman was diagnosed with dementia with probable CTE. He is joining the lawsuit that other players of his generation are bringing against rugby’s governing bodies.

The sport has been rocked by these diagnoses – and Hayman’s resonates as the first for an All Black of that generation. In 2001 he became All Black No 1,000 and went on to win 45 caps, before spending the second half of his career in Europe, joining Newcastle in 2007 and Toulon in 2010. He won three European titles and one French with the latter.

“I was a commodity, and I understood that,” he says of his playing days. “It’s like that scene in Saving Private Ryan, when the guy tells the bloke with shell shock: ‘When you can accept you’re dead, you can function as a soldier.’ That rang true from a rugby point of view. Once you accept your body’s screwed and you have no respect for it, you become an awesome player. Now I’m sort of paying the price a wee bit.”

Related: Rugby’s card-happy approach to concussion is just not working | Michael Aylwin

So far, the cameras and microphones have been trained on the players themselves, as they search in their confusion for answers, reassurance and support. But it is the families who are really rocked when dementia descends. It is the families who pick up the pieces when a sport is done with its heroes. They are the ones to interview if a true account of this terrible affliction is the aim.

“I started going out with someone who I’ve got a baby and a business with, who then gets diagnosed with CTE, which is this long-term, life-changing pain in the arse. It takes over everyone’s lives completely. Every day Carl’s head hurts. Every day he struggles to remember what he’s doing. He has regular bouts of anger and then regret for his anger. He doesn’t want to be here. I’m not enjoying him being here …”

The only recourse at such times is the reminder to self that this is a disease at work, not the person with whom you chose to share your life. The tenderness returns to Matthews’ voice as she describes what is happening in Hayman’s brain.

“The way it has been explained to us is that you’ve only got so much energy to use in a day. When you have a brain injury, rather than a brain connection going from A to B, which is two calories, yours has to go from A to Z to X to Q, P, R and B – and that takes up 20 to get the same outcome. You and I can have this conversation and it’s not even registering on our calorie count, but for Carl, his eyes are going, ‘I need to focus,’ his ears, ‘I need to listen’, then he has to process, then he has to speak. To do that, his poor brain has to go all around the stops, because there’s a big block of protein that’s built up in there, stopping the connections.”

Inevitably, executive function declines. Hayman is meant to run the boatshed side of their business, while Matthews runs the commercial, but increasingly she is doing both. “You send him shopping, and he comes back with half the things you need, and you can see the pain on his face from the shopping that he’s sort of half-done. It’s the same with buying oil for the boat or life-jackets. Just let me do it. The repercussions and the pain it puts him through and what I have to do to rectify whatever he’s done – it’s just easier if I do it.”

And then there is the vast wall of systemic barriers to support, or even just to knowledge of one’s entitlement to it. This can overwhelm the most able-minded; someone with dementia and no partner to vouch for them would not stand a chance. In New Zealand, Matthews has found the Accident Compensation process (ACC) as torturous and labyrinthine as such public institutions the world over. Meanwhile, rugby’s governing bodies are keeping their heads down with a lawsuit pending.

Has New Zealand Rugby offered support since Hayman went public with his diagnosis? “Are you joking?” says Matthews.

Since his diagnosis, life has been made easier by the engagement of an occupational therapist to assist Hayman with everyday tasks and a neuropsychologist to process how he’s feeling and to control the rage and changes in emotion that are bound up with dementia. “I’ve funded all of my own care,” he says. “I’m really lucky, because I made a bit of money out of the game, so I’m in a place where I can fund these things. But there’s a big issue here. We need to put stuff in place for players. It’s almost as if the game wants to avoid the fact this even exists.”

New Zealand Rugby has not responded to the Guardian’s request for comment. On Monday, World Rugby did announce a tweak to rugby’s minimum return-to-play protocol after a diagnosed concussion, described as “long overdue” by campaigners. And on Friday the Alzheimer’s Society in the UK announced an encouraging partnership with the players’ associations of rugby, football and cricket to provide support for those diagnosed with dementia.

Dementia is not only devastating but insidious. There is never a neat point at which a diagnosis is obvious and incontestable, and there is certainly never a single incident that can be pinpointed as the cause, as there is for other injuries with long-term consequences. It may be obvious that rugby is the cause, but it remains impossible to prove to, for example, ACC’s satisfaction. Hayman was diagnosed with concussion only once in his career, in 2006 against Australia.

Rugby has yet to come to terms with the crippling realisation that something as manageable as concussion, however arbitrarily it is defined, is not the cause of CTE. Hayman’s case, with a history of just one diagnosed concussion, is simply the latest to demonstrate that the root of the problem is the uncountable number of times a brain is rattled over a long professional career.

“But how do you prove that his CTE is the result of his playing in New Zealand, when that is only half of his career? There are no records of him suffering head injuries, because he wasn’t concussed,” says Matthews. “There are no records of a head bang, because you’re getting your head banged the whole time, impact after impact. There’s just a record of that one concussion in 2006. Then they say: ‘Oh, you didn’t go to see a doctor in Newcastle, and you have no medical records from Toulon …’”

This sort of impasse is familiar to anyone negotiating the murky sphere of dementia, where the first creeping symptoms are non-specific and very often shared with other conditions that might be treatable and not terminal. Only those at close quarters with the patient – in other words, the family – are in any position to notice. And even they cannot really be sure, unless and until some great schism in the daily routine puts it beyond doubt.

There will be more and more rugby players scattered around the globe, hopefully most with families to support them, who find themselves coming to terms with the legacy of their years in the game. Rugby has not – and probably cannot afford to – acknowledge a direct link between the sport and CTE – hence that lawsuit. But Hayman qualifies to join the action only because of the three years he spent playing in England, at Newcastle. If rugby’s CTE crisis is as severe as seems likely, many others will languish for now in limbo.

Even the CTE aspect is clouded in uncertainty, hence the qualification of “probable” to the diagnoses. CTE cannot be confirmed until the brain is dissected post-mortem, although science is working on that problem. What is beyond dispute is that these players have brain damage that requires management. The question is whether their conditions are degenerative. The evidence from America, where their football is a few decades ahead of both codes of rugby as a full-time collision sport, is not encouraging, but decades is what it will take to know for sure.

Which means more uncertainty for those already floundering. The posturing between sport, science and law will continue, but that is of little consolation to those living with these conditions now.

“The brain illnesses,” says Matthews, “are definitely worse than the cancers or whatever, where you’re either going to survive or die in the next two years. Dementia could go on forever. And to lose the capacity to be who you were is devastating.”

Devastating for your family to lose who you were too. Kiko Matthews is not afraid of a challenge, which is just as well. In a sane world, she would not have to fight for help with it.

Samaritans can be contacted on 116 123 or email jo@samaritans.org or jo@samaritans.ie. In the US, the National Suicide Prevention Lifeline is at 800-273-8255 or chat for support. You can also text HOME to 741741 to connect with a crisis text line counselor. In Australia, the crisis support service Lifeline is 13 11 14. Other international helplines can be found at www.befrienders.org