During all the difficult moments I went through when leaving my husband of 20 years and moving out of our family home, at no point did I envisage it would be a missed John Lewis delivery that would break me. Yet here I was – day one in the flat I had rented and, for reasons too mundane even to go into, with just a mattress on the floor for a bed. I burst into tears, saying to myself, 'This is just not fair. I'm 50 years old and I don't even have a bed – it wasn't meant to be like this.'

Much as I had wanted to leave my marriage, in that moment, I felt so overwhelmingly alone. I can imagine for many women in a similar situation, this might make them retreat back to a safe, if unhappy, marital home.

People talk about all the Big Decisions around divorce – what to say to your children, how to keep it as amicable as possible. No one tells you that a trivial practicality like making sure you have furniture – and being in for the delivery while also working on a job two hours away – can be the thing that trips you up.

When I left my husband, I thought I had considered every last detail – from the huge (the impact on my kids) to the mundane (I'll need to buy a toaster) and yet I still had moments where, out of nowhere, an unexpected pitfall threatened to derail me. I did not see that coming.

This is precisely why my advice to anyone who might be thinking of leaving is this: get your ducks in a row beforehand. Envisage every eventuality and then work out how you would deal with it.

Partly because you will need to make toast in your new home but more importantly because if anyone – friends, your ex – asks, 'Well, what are you going to do about x, y, z?' and your response is, 'Oh, I don't know', then your confidence will start to slip away. Suddenly, going it alone feels too difficult. I know women who have chosen to stay in an unhappy marriage because the practicalities of leaving are too daunting.

I consider myself a capable person – in my married life I organised everything, so I assumed I'd be fine. But I hadn't considered how something as mundane as renting a flat can floor you. I hadn't had to do it since I was about 24 and I wondered, how do you rent a flat?

I hadn't thought about stupid things like getting references (from where, when you haven't been a tenant in over 20 years?) and all the forms. When you're suddenly a team of one, the logistics can feel like a pretty lonely full-time job.

Kat Farmer said although she considered every detail when she left her husband, she still had moments where, out of nowhere, an unexpected pitfall threatened to derail her

Waves of emotion will hit you at the most unlikely times, too. I didn't take any of the basics from my marital home, so I had to buy almost everything from scratch. Then, in the midst of a very practical 'cutlery and kettle' shopping trip, I found myself welling up over a hideous teapot. Why? Because I loved it in all its gaudy kitschness – and my ex-husband would have detested it. That's when the grief hit me. The end of a marriage – even if you know to your very core that you'll be so much happier apart – does feel like a sort of grief. It's mourning the life that you thought you could have had; the marriage that you wanted but never really got. For me, it was the sadness of thinking, what if I'd been married to a person who'd have loved this teapot as much as I do? Maybe it could have been different.

Not long after I had moved into my rental flat, I saw a mouse in the kitchen. I am not good with mice and ended up sitting on the countertop for three hours, watching for it. Thank god I had a bottle of wine because I could not get down from that counter. I don't even know what my ex-husband would have done, but things like that just feel easier when you've got someone there to bounce off. Luckily, Instagram came to my rescue – I posted on my Stories that I was trapped and somebody handily said, 'If you give it a name, it'll go away and won't come back'. So my mouse became Derek and I genuinely never saw him again. I don't know why. Superstition maybe? Let's not argue with the magic.

All of these experiences have taught me how to ask for help, and how to accept it when it's offered – which is not easy for someone as independent as I am. I've had to learn it's not a sign of weakness. That said, there is no substitute for being able to manage the simple things yourself.

I know women who don't fill up their own car with petrol because they don't know how. A friend of mine was getting divorced and one time his ex-wife rang him to say she didn't know how to put air in her tyres and he needed to help. I was gobsmacked. I would rather ring Putin for a cosy chat than phone my ex-husband and ask him to put air in my tyres!

That first night in my flat, I called in my secret weapon – my gang of girlfriends. And this is my final piece of advice: have good friends around you who will literally swoop in. The best girlfriends, in my experience, are the ones who are either divorced or going through a divorce, because they empathise. They've been there and intuitively know what you need before you do.

I had been saying to them, 'I'll be fiiiine on my own' – but they knew better. So listen to the people who have already been there. My friends came over with champagne and they bought me a vase, because, of course, I didn't have one. (Why would I, when I didn't even have a kettle?) They made sure I wasn't alone that first night – I genuinely thought I'd be OK, but they knew I wouldn't, not really.

My friends are the ones who have picked me up. They are my support network, my sounding boards, my advice-givers and the people I have cried and cried on. When you go through something like this together, it bonds you in a way that will never break.

Hiding from a mouse called Derek may have been a low point – but let me tell you, when my boiler broke and I worked out how to fix it all by myself, I felt superhuman! There's no more empowering feeling that taking control of your own life like that. And for everything else, there's always good friends and champagne.

• If you have any questions you'd like to ask Kat or topics you want her to cover, write to her at editor@you.co.uk