The porter turned to us with the regretful face of someone who is about to deliver bad news for which he is not personally responsible, and explained that out of me and Mark, only one of us could go further. He was sorry. But those were the rules.

Mark didn’t hesitate.

‘You go,’ he said. ‘I’ll wait.’

I had never been as grateful to him as I was at that moment. To make that decision so calmly and quickly, without complaining, to make it easy for me to go on… Whatever might lie ahead, and whatever he might have done or not done in the past, I knew right then that he would always have my back.

There was no time to lose. I said a hurried goodbye to Mark and followed the porter and the cot with Felix on it through the silver doors into the small, windowless room reserved for patients to be prepared for surgery.

It was like the airlock of a spaceship, a space between doors to different worlds. On the other side of one door was the rest of the hospital, and Mark, waiting. And the other door led to the operating theatre, where I would not be able to follow. This was as far as I could go: after this I, too, would have to turn back, and wait.

The anaesthetist was already there, waiting. The porter went out, and the anaesthetist invited me to sit and showed me the consent form that had been prepared for me to sign.

He was a little younger than me, brainy-looking, wide-eyed and sincere in his surgical scrubs, and he spoke gently and slowly as he set about explaining the possible risks and side-effects of the procedure Felix was about to undergo. I could feel him willing me not to panic or give in to hysteria, to take in what he was saying as calmly as he was saying it, and then to sign the form so they could go ahead and do what was necessary to save Felix’s life.

It wasn’t reassurance he was offering, though. It was anything but reassuring. What he was doing was making clear that there was a choice, and I had to make it. And the choice was between risk and death, and there were no alternatives.

Felix was still awake, but only just. There was a mobile hanging on the wall opposite him, projecting colours on the wall behind it: something soothing for children to watch before slipping into unconsciousness.

I said, ‘I don’t care what the risks are. If this is his only chance, I’ll sign.’

And I did. Then I reached out to touch Felix’s tiny hand and his eyes flickered open and closed again. The anaesthetist put a mask over his face and I felt Felix reeling away from me, sinking into darkness.

I took one last look at him: his soft cheeks, the fluff of downy hair on the top of his head, his miraculous eyelashes. I said, ‘Goodbye, my love.’ And then I had to leave. I turned away from him and went the opposite way to the way he would be going, through the double doors back to the corridor.