At 6.50am on Saturday, I text my friend Esther: "So sorry, but I've woken up feeling rotten and don't think I'll be able to make it out tonight." I feel guilty about cancelling our plans for the evening, but better about having done it so early on in the day: at least Esther will have time to find another friend to meet.

Sometimes I wish I was a workaday version of Doctor Who: a time traveller, but without the special effects and the fear of baddies. Then I could predict how to live from one hour to the next, with the knowledge of how things could, or would, turn out. Hindsight is all very well, but at present I am not using it to any effect. I can't seem to act in my own best interests, despite knowing that often my actions interrupt the fun I could be having.

Quite why I have blown Esther out is questionable. Yes, I'm tired, but so are most parents. I've got a bit of a cold and a headache, but not the type that feels like a bassoon permanently playing in my head. It's more about the things going on around me, than me, and I wish I could separate the two. The Doctor could go out and have fun, solve the mystery and fend off the bad guys before bedtime. I can do none of these things.

I am sure that by 7pm – when the children will be fractious, bored and tired – I'll regret my decision to stay at home. I'll watch the buses at the end of our street gliding into town and I'll want to run out of the door and hop on for the ride. Now, however, I am conscious of something brewing in my stomach like bad ale: I am not physically unwell. I simply feel after weeks of holding it together that, suddenly, I am not.

R spent the night away in a hotel – something he does when he works late and has to be in the office early – and I have woken up in our double bed alone, restless.

My phone pings – a text from Esther: "Oh, what a shame. Hope you're OK. Call me if you feel better or change your mind." Even as I read this, I plot a miraculous recovery. I want to reply: "I'm actually not really feeling very ill now. In fact, I never was. Can we go ahead with the original plan?"

But I don't because my sudden change of heart might seem bonkers. I roll out of bed to the sound of the youngest one chanting, "I done a poo." This sets the tone for a day that, like most Saturdays as the only adult among children, will contain its fair share of shits, giggles and low-rent entertainment.

I lay the table for breakfast, my son already scooping Cheerios and milk into his mouth with his hands. I join in as he counts cereal pieces, correcting him as he misses out two or three numbers on his way up to 10. All the while I am distracted by R: I mime along to the words of all sorts of conversation perfectly. My mind, however, is elsewhere, consumed almost entirely by my husband, despite his absence.

I imagine R in his hotel room, a colossal concrete slab overlooking the Thames. I wonder if he's lying in, lying to me about having to be up early. I wonder if he has a hangover, with a convenient 24 hours to be able to shake the evidence from his body before he comes home to us, his family, tomorrow.

The problem with a major relapse is this: the stuff that R confesses when he is sober is both a blessing and a curse: it sometimes sates my over-anxious mind and makes me feel that I am his true confidante. But it can also reveal things that I had little knowledge about before. Was I aware that he took cocaine most weeks? Did I know that he had hit on a girl we both knew when he was drunk before? No, I did not. But now I do, and there is no telling if he will do these things again and this is a burden I cannot shake.

In a sense, when R relapsed a few weeks ago, I relapsed too. I started to forget myself and the family; now I am becoming increasingly distant.

Impulsively, I pick up my phone and decide that the day must belong to the children and me once more. I text Esther.

"I do feel a bit shitty, but I'm more tired than anything. The babysitter's still booked, so if you haven't already made other plans, I'd love to meet up."