The conversation you didn't

She said it on a Wednesday night and I genuinely thought she was about to ask me to take the bins out. The cognitive dissonance is what I remember most. The words "I don't want to do this anymore" did not parse, like a sentence in a language I almost knew.

If you're reading this, you're probably in the bit where the world has changed and your body hasn't caught up. The fridge still hums. The kids still need lunch tomorrow. Somebody, you presume, will still go to work in the morning. Yourself, in fact.

This is the article for the man who didn't see it coming. Or saw it coming and lied to himself about it for so long that arrival still felt like ambush.

The first 72 hours are not for thinking

Your prefrontal cortex is offline. The decisions you make right now will, in retrospect, look like the decisions of a stranger. So don't make any.

A short list of things to NOT do in the first three days:

• Don't beg.
• Don't promise to change everything by Friday.
• Don't move out in a rage at midnight.
• Don't agree to anything in writing.
• Don't sleep with anyone.
• Don't tell the kids alone, while she's at her sister's.
• Don't get drunk and call her parents.
• Don't post anything anywhere.
• Don't book a holiday "to think." You'll just bring the thinking with you and add airfare.

The instinct to act is just your nervous system trying to make the pain mean something. Acting will not relieve it. Sitting with it, badly, awkwardly, with the lights on, will.

If you can take two days off work, take them. Not for processing. For not making decisions in front of colleagues while running on three hours of sleep. If you can't take time off, lower the stakes of every conversation you have. Postpone the meetings that can be postponed. Decline the after-work drinks. Buy yourself the smallest possible week.

The stories you'll start telling yourself

Within 24 hours your brain will offer you four stories. None of them are fully true. All of them are partially true. The trouble is choosing one as the whole picture.

• The villain story. She did this to me. There's another bloke. She was always cold. (Sometimes true. Often partial.)
• The victim story. I gave her everything. I don't deserve this. I don't understand. (Sometimes true. Often partial.)
• The collapse story. I should have seen it. I missed every sign. I am a fool. (Sometimes true. Often partial.)
• The redemption story. If I just change X by Tuesday, this is fixable. (Almost never true at this point.)

Notice them. Name them. Don't act on any of them yet. They will all turn into something more useful in three months. Right now they're just brain weather. Treat them like passing thoughts, not as facts to build a campaign on.

The story you eventually settle into will probably be a quieter, more honest version that doesn't fit any of the four. That story takes time to arrive. Six months, sometimes longer. Don't rush it.

What you can do

Three things, in order. Nothing else.

• Move your body once a day. A walk counts. A bike counts. The gym counts. Lying in bed scrolling does not count.
• Eat one proper meal a day. Not a meal-deal. Something with vegetables.
• Tell ONE person you trust, in person, what is happening. Not the group chat. Not LinkedIn. One person.

That's it. The rest of the day is for surviving until tomorrow. Rinse, repeat, until day seven.

If you can add a fourth thing, make it sleep hygiene. Phone out of the bedroom. Lights down by 10pm. Boring routines. The body doesn't care that the marriage is ending. It still needs the same eight hours, and it'll struggle to get them. Anything you can do to give the body a fighting chance is worth doing.

The questions you cannot answer yet

You will be desperate to know things. Is it final? Is there someone else? Will we get back together? Should I keep wearing the ring? Where will the kids sleep on Saturday?

Most of these questions cannot be answered yet, by either of you. Pushing for answers in the first fortnight produces lies, half-lies, or commitments she will retract by week three. Let the questions exist without forcing answers. This is the hardest single thing.

If you must ask one question in week one, make it this one: "Can we agree not to make any big decisions for two weeks?" If she says yes, you have a runway. If she says no, you have information.

The questions will resolve themselves on a longer timeline than you want. Some by week six, some by month three, some by month nine. The order in which they resolve is not under your control. Trying to control it is the source of most of the worst decisions made in the first month.

What to tell the kids

If you have kids, they will ask. The honest baseline is: "Mum and I are working out something hard between us. It is not your fault. We both love you. Nothing is changing tonight."

That last sentence is the load-bearing one. It buys you time to get the longer story right. Don't tell them more than you and your partner have agreed to tell them, even if your partner isn't currently agreeing on much.

If she has already left, or things are openly hostile, say less rather than more. "Mum is staying somewhere else for a bit. We are still working it out. We'll tell you more when we know more." That is honest. It is also enough.

The man you'll be on day 30

Here's the only useful thing I can offer from the other side. The man you are at hour 36, frozen, googling, ten kilos of grief in a chest that doesn't fit it, is not the man you'll be at day 30. Not because the pain leaves. Because the body adapts.

The shock is the most acute it will ever be in the first week. Do not make decisions from inside it. Do not let anyone else make decisions for you from inside it either.

Survive the week. Walk every day. Eat once properly. Tell one person. Sleep when you can.

You did not see this coming. You are still here. That counts.

Breathe. Wait. Decide later.