Sarah Tarlow built her academic career as an archaeologist researching grief and mourning. Archaeologists have always studied bodies, but Tarlow’s interest is in “mortuary and commemorative practices”, the relationships between the living and the dead. Some of the bodies unearthed by her peers tell stories of care: people who lived many years with injuries or diseases incompatible with survival in the absence of constant attention from others. These finds, Tarlow says, are regarded as evidence of selflessness, even humanity itself, though other mammals behave similarly and caring for someone disabled is not necessarily a purely altruistic act. Now she has written her own memoir of care, followed by the remaking of the relationship between the survivor and the deceased.

In 2013, Mark, Tarlow’s partner of 15 years and the father of her three children, developed the first symptoms of a degenerative disease that was never fully diagnosed. In May 2016, while Tarlow and her children were out on a rare family visit, Mark took a fatal overdose of a drug he had bought online and kept hidden until he judged he’d lost enough to be sure about ending his life while still being able to do it. It was not, Tarlow insists, an irrational decision. Mark was not mentally ill: “Being dead is sometimes better than being alive.”

She played no part in his death, and the arrangements he made were plainly intended to leave no doubt as to her ignorance. All the same, she cannot regret his passing – because Mark was in terrible and worsening pain, had lost his capacity to do anything he found pleasant or meaningful, and expected only further deterioration.

The story recalls Amy Bloom’s In Love, the memoir of that writer’s husband’s death at Dignitas, but there are crucial differences. Mark died alone, because Tarlow’s presence or knowledge would have made her guilty under English law. “Did he call for me, for his mother, for anyone to hold his hand while the darkness filtered in?” she wonders. It’s possible he would have chosen to die later had assistance been available.

For Tarlow, the labour of care had been overwhelming. Mark’s cognitive impairments had made him hostile and aggressive towards the children and their friends as well as his partner. There were few visitors or outings and no respite. The NHS could keep Mark alive and supply Tarlow with hoists and rails so she could move him around their Victorian house, but there were no sociocultural resources: “We are very bad at supplying the community, the human contact, that would compensate for the things our science and technology cannot do.”

We have a burgeoning literature of care and grief, but this book is unusual in its critique of the whole idea of unpaid care. It’s not always rewarding. Not all relationships work that way, especially when they were already in difficulty: “I could not easily love him when he was caustic and wounding to the children.”

Tarlow is frank about her resentment and despair, and also about her guilt over her resentment and despair. She is clear-sighted about what the rest of us have invested in ignoring carers’ misery – because if we recognised that many people do not find it worthwhile to give up their careers and friendships and health to look after relatives, we would see that “as a society, we build our ability to function on a foundation of unhappiness”.

This book will be divisive because ambivalence in caring for the dying is as much of a taboo as ambivalence in caring for babies used to be. “I wish the character of me was a bit nicer,” Tarlow writes, and one sees why. But the narrator has the scholar’s inability to soften or sweeten what she knows, which is that we don’t always love the dying and the dead, and that rage and mixed feelings are at least as interesting as sorrow. Look elsewhere for cheeriness; the pleasures offered here are those of intelligence and complexity in the hard times that will come to many of us.

• The Archaeology of Loss by Sarah Tarlow is published by Picador (£16.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply.