Keeping the promise he had made, Mark Sanderson killed his terminally ill lover by smothering him with a pillow. His new book examines the context and aftermath of an act he feels was emotionally right but intellectually questionable, writes Robert O'Byrne

At almost exactly the same time as Diane Pretty died in England last month, a book appeared which had considerable relevance to her circumstances. Suffering from motor neurone disease for the previous decade, Pretty had fought a legal case through the British legal courts and on to the European Court of Human Rights.

She wanted her husband, Brian, to help her commit suicide without him being liable to prosecution. The couple consistently lost their case and Pretty eventually died without any assistance from her family.

Meanwhile, coincidentally, journalist and author Mark Sanderson published a memoir, Wrong Rooms, in which he describes how, eight years ago, he helped his lover, Drew Morgan, to die. In accordance with a promise made to Morgan when terminal cancer had been diagnosed, and with his approval when the moment arrived, Sanderson smothered Morgan and "kept the pillow there long after the bucking had stopped".

The couple had met less than two years earlier and, shortly before sickness intervened, Sanderson wrote in his diary that he was experiencing "one of the very best periods of my life". Much of the memoir is taken up with the grim banality of dealing with doctors and hospitals and the paraphernalia of serious ill-health, and this helps to explain why Sanderson chose to keep the promise he had made to Morgan. It is a shock to read that he attempted to smother his lover twice; on the first occasion, the latter fought back, crying: "Not yet. Not yet. I'll let you know when, somehow."

A few days later, he did convey to Sanderson that the moment for release had arrived.

Wrong Rooms is a remarkable book, and not simply because of the author's frankness. Since the 1980s, what might be considered a minor genre of memoirs has emerged in which gay men describe the deaths of their partners, usually from an AIDS-related illness. The appeal of such works is almost exclusively to other gay men, but this is most certainly not the case with Wrong Rooms. The sexuality of Sanderson and his late lover is almost an irrelevance and the story he tells ought to find a response among all readers who have experienced loss through death.

The author is keen to stress this aspect of the book, rather than the potentially titivating details of his involvement in Morgan's end.

"I was writing a love story, not a murder story," he says.

Nevertheless, he accepts that "some people will say that I have committed a crime". Through his solicitor, the police in England were notified in advance of the book's publication and "so far there has been silence; they said they would inform us when and if they received a complaint".

Sanderson does not believe himself to be a criminal: "There was no malice aforethought and Drew wanted me to do it." However, it is clear that he suffered greatly not just from his lover's death but also from having participated in that event.

During the following years, he drank very heavily, became temporarily dependent on cocaine, suffered from deep depression and attempted to commit suicide. He now accepts that although he was only fulfilling the wishes of Morgan, "after a while, there was a conflict in me between the head and the heart. Emotionally, I knew I'd done the right thing, but intellectually I wasn't sure; it's not true that I have felt guilty, but the conflict is still there. That did make the process more difficult - and prolonged it for me."

The intensity of his response to Morgan's death does not necessarily strike him as extreme. "Some people may think it so, but I don't. Of course, I've only been through all this once and have nothing to compare it with, but if you love someone heart and soul, how are you supposed to react?"

Sanderson says one reason he wrote Wrong Rooms was precisely to help him resolve his feelings about Morgan and the manner of his death. But "I didn't want it to be sentimental; there's no special pleading. I wanted to tell the story as honestly and as impartially as possible, trying to adopt a professional journalistic stance towards myself".

Maybe so, but both in his book and in conversation, Sanderson cannot be impartial about the ability of modern medicine to keep terminally ill patients alive for longer than they wish.

"What's the point?" he asks. "Why prolong life when it's patently not worth living? I think that's cruel. Some people don't want to suffer, and being forced to undergo that is torture. If we all have a right to life, we should have the right to end it when and how we choose."

At the same time, "personally speaking, I don't think my book can be taken as promoting euthanasia. I never use the word in the book and in fact I think what I have written warns of its perils".

Thanks to ongoing advances in medical science, Sanderson's predicament is likely to become more common in the years ahead. Perhaps this is why even "people who've said they can't condone what I've done say they do understand why I did it".

Until the book was published, "nobody really knew what had happened between Drew and myself. It was an overwhelming experience, but I'm starting to come out of it. Of course, there's still a small part of me even now waiting for him to come back. But I know he's not going to do so."

Wrong Rooms by Mark Sanderson is published by Scribner at £15.99 sterling