9st, alcohol units 4, cigarettes 6, calories 2746, correct lottery numbers 2 (v,g.).

At last I got to the bottom of Mum and Dad. I was beginning to suspect a post-Portuguese-holiday Shirley-Valentine-style scenario and that I would open the Sunday People to see my mother sporting dyed blond hair and a leopard-skin top sitting on a sofa with someone in stone-washed jeans called Gonzales and explaining that, if you really love someone, a forty-six year age gap really doesn't matter.

Today she asked me to meet her for lunch at the coffee place in Dickens and Jones and I asked her outright if she was seeing someone else.

'No. There is no one else, she said, staring into the distance with a look of melancholy bravery I swear she has copied from Princess Diana.

'So why are you being so mean to Dad?' I said.

'Darling, it's merely a question of realizing, when your father retired, that I had spent thirty-five years without a break running his home and bringing up his children – '

'Jamie and I are your children too,' I interjected, hurt.

' – and that as far as he was concerned his lifetime's work was over and mine was still carrying on, which is exactly how I used to feel when You were little and it got to the weekends. You only get one life. I've just made a decision to change things a bit and spend what's left of mine looking after me for a change.'

As I went to the till to pay, I was thinking it all over and trying, as a feminist, to see Mum's point of view. Then my eye was caught by a tall, distinguished-looking man with grey hair, a European-style leather jacket and one of those gentleman's handbag things. He was looking into the cafe, tapping his watch and raising his eyebrows, I wheeled round and caught my mother mouthing, 'Won't be a mo,' and nodding towards me apologetically.

I didn't say anything to Mum at the time, just said goodbye, then doubled back and followed her to make sure I wasn't imagining things. Sure enough, I eventually found her in the perfume department wandering round with the tall smoothie, spraying her wrists with everything in sight, holding them up to his face and laughing coquettishly.

Got home to answerphone message from my brother Jamie. Called him straight away and told him everything.

'Oh, for God's sake Bridge,' he said, roaring with laughter. 'You're so obsessed with sex if you saw Mum taking communion You'd think she was giving the Vicar a blow-job. Get any Valentines this year, did you?

'Actually, yes,' I breathed crossly. At which he burst out laughing again, then said he had to go because he and Becca were off to do Tai Chi in the park.

8st 13 (v.g. but purely through worry), alcohol units 2 (but the Lord's Day), cigarettes 7, calories 2100.

Called Mum up to confront her about the late-in-life smoothie I saw her with after our lunch.

'Oh, you must mean Julian,' she trilled.

This was an immediate giveaway. My parents do not describe their friends by their Christian names. It is always Una Alconbury, Audrey Coles, Brian Enderby: 'You know David Ricketts, darling – married to Anthea Ricketts, who's in the Lifeboat.' It's a gesture to the fact that they know in their hearts I have no idea who Mavis Enderby is, even though they're going to talk about Brian and Mavis Enderby for the next forty minutes as if I've known them intimately since I was four.

I knew straight away that Julian would not turn out to be involved in any Lifeboat luncheons, nor would he have a wife who was in any Lifeboats, Rotaries or Friends of St. George's. I sensed also that she had met him in Portugal, before the trouble with Dad, and he might well turn out to be not so much Julian but Julio. I sensed that, let's face it, Julio was the trouble with Dad.

I confronted her with this hunch. She denied it. She even came out with some elaborately concocted tale about 'Julian' bumping into her in the Marble Arch Marks and Spencer, making her drop her new Le Creuset terrine dish on her foot and taking her for a coffee in Selfridges from which sprang a firm platonic friendship based entirely on department store coffee shops.

Why, when people are leaving their partners because they're having an affair with someone else, do they think it will seem better to pretend there is no one else involved? Do they think it will be less hurtful for their partners to think they just walked out because they couldn't stand them any more and then had the good fortune to meet some tall Omar Sharif-figure with a gentleman's handbag two weeks afterwards while the ex-partner is spending his evenings bursting into tears at the sight of the toothbrush mug? It's like those people who invent a lie as an excuse rather than the truth, even when the truth is better than the lie.

I once heard my friend Simon canceling a date with a girl – on whom he was really keen – because he had a spot with a yellow head just to the right of his nose, and because, owing to a laundry crisis he had gone to work in a ludicrous late-seventies jacket, assuming he could pick his normal jacket up from the cleaner's at lunchtime, but the cleaners hadn't done it.

He took it into his head, therefore, to tell the girl he couldn't see her because his sister had turned up unexpectedly for the evening and he had to entertain her, adding wildly that he also had to watch some videos for work before the morning; at which point the girl reminded him that he'd told her he didn't have any brothers or sisters and suggested he come and watch the videos at her place while she cooked him supper. However, there were no work videos to take round and watch, so he had to construct a further cobweb of lies. The incident culminated with the girl, convinced he was having an affair with someone else when it was only their second date, chucking him, and Simon spending the evening getting hammered alone with his spot, wearing his seventies jacket.

I tried to explain to Mum that she wasn't telling the truth, but she was so suffused with lust that she had lost sight of, well, everything.

'You're really becoming very cynical and suspicious, darling.' she said. 'Julio' – aha! ahahahahahaha! – 'is just a friend. I just need some space.'

So, it transpired, in order to oblige, Dad is moving into the Alconburys' dead granny's flat at the bottom of their garden.

V. tired. Dad has taken to ringing up several times in the night, just to talk.

9st, alcohol units 2, cigarettes 9, fat units 8 (unexpectedly repulsive notion: never before faced reality of lard splurging from bottom and thighs under skin. Must revert to calorie counting tomorrow).

Tom was completely right. I have been so preoccupied with Mum and Dad, and so tired from taking Dad's distraught phone calls, I have hardly been noticing Daniel at all: with the miraculous result that he has been all over me. I made a complete arse of myself today, though. I got in the lift to go out for a sandwich and found Daniel in there with Simon from Marketing, talking about footballers being arrested for throwing matches. 'Have you heard about this, Bridget?' said Daniel.

'Oh yes,' I lied, groping for an opinion. 'Actually, I think it's all rather petty. I know it's a thuggish way to behave, but as long as they didn't actually set light to anyone I don't see what all the fuss is about.'