We were chatting about N's love life, what else is new? It looks as if things are decidedly Off with off-again on-again girl. I find people who are incapable of making decisions irritating in general - and her irritating in particular. Especially knowing that she still expects him to drop everything and come round as and when she wants, take her out for a meal and morose conversation, then drop her back home without so much as a blowjob. Some women have no shame. 'You need to think about where this is going,' I said. 'You're letting her set the tone and you just go with it. She's using you, and it's not right.'

'Yeah, I knew you'd say that,' N said. 'But I have this theory. The Quantum Theory of Relationships.'

'You are going to have to explain that,' I said. 'I'm in the bath, it's brain hibernation time.' After a nighttime run, especially in winter, nothing hits the spot like submersion in a hot bath. Nothing. Not even sex.

'Come on, you're a clever girl. You know what I mean.'

I wiggled my toes in the bubbles at the far end. The cat was sitting on the bath rack, eyes half shut, enjoying the steam. He swiped halfheartedly at my feet. 'Know what you mean? Honey, I barely know my Lavoisier from Courvoisier.'

He laughed. 'In a nutshell, it's this. You can't observe a relationship without changing it. If I stop to think about the whys and wherefores, it's destined to fail. I'm happy to let what happens happen for the moment.'

'I like it. Is this another one for N's Little Book of Relationships?'

'Yeah, okay. That brings us up to, what, two pages now?'

'Short enough the get it out in time for Christmas.'

'Now you're talking.'