‘Out,’ I said, still holding her. ‘Give me the keys and get out.’ It was as if I’d never cared for her at all. I wanted to wipe her away. I wanted to blot out her blazing stupid face. She didn’t deserve this, in a corner of my mind I knew it was my weakness not hers that had brought us to this shameful day. I should have smoothed things down, parried, instead I slapped her across the face and tore my keys from her pocket.

‘That was for the bathroom,’ I said as she felt her bleeding mouth. Jacqueline stumbled towards the door and spat in my face. I took her by the collar and frog-marched her to her car. She skidded away without her lights on.

I stood watching her go, hands limp at my sides. I groaned and sat on the low wall beside my flat. The air was cool and calming. Why had I hit her? I’d always prided myself on being the superior partner, the intelligent sensitive one who rated good manners and practised them. Now I’d shown myself to be a cheap thug in a scrap. She’d angered me and I’d responded by thumping her. How many times does that turn up in the courts? How many times have I curled my lip at other people’s violence?

I put my head in my hands and cried. This ugliness was my doing. Another failed relationship, another hurt human being. When was I going to stop? I pulled my knuckles along the rough brick. There’s always an excuse, a good reason for behaving as we do. I couldn’t think of a good reason.

‘All right,’ I said to myself. ‘This is your last chance. If you’re worth anything show it now. Be worth Louise.’

I went back inside. Louise was sitting very still looking at the glass between her hands as though it were a crystal ball.

‘Forgive me,’ I said.

‘You didn’t hit me.’ She turned to me, her full lips in a long straight line. ‘If you ever do hit me I shall leave you.’

My stomach contracted. I wanted to defend myself but I couldn’t start to say anything. I didn’t trust my voice.

Louise got up and went to the bathroom. I didn’t warn her. I heard her open the door and draw in her breath sudden and sharp. She came back and held out her hand. We spent the rest of the night cleaning.

The interesting thing about a knot is its formal complexity. Even the simplest pedigree knot, the trefoil, with its three roughly symmetrical lobes, has mathematical as well as artistic beauty. For the religious, King Solomon’s knot is said to embody the essence of all knowledge. For carpet makers and cloth weavers all over the world, the challenge of the knot lies in the rules of its surprises. Knots can change but they must be well-behaved. An informal knot is a messy knot.

Louise and I were held by a single loop of love. The cord passing round our bodies had no sharp twists or sinister turns. Our wrists were not tied and there was no noose about our necks. In Italy in the fourteenth and fifteenth centuries a favourite sport was to fasten two fighters together with a strong rope and let them beat each other to death. Often it was death because the loser couldn’t back off and the victor rarely spared him. The victor kept the rope and tied a knot in it. He had only to swing it through the streets to terrify money from passers-by.