Partings, reunions and thirds.

A relationship is kept in first place, or quietly pushed down the list, in small daily moments: how you part, how you come back together, and what you allow to come between you.

Everyone reacts to partings

Tatkin asks you to see a relationship as a long string of partings and reunions. Going to work, to the shops or just to another room: each is a small separation followed by a small return.

Everybody reacts to these, he says, but not everybody knows it. Waves react openly: they miss their partner and may find it hard to get going until the other is back. Islands look as if nothing is happening, yet he insists they are affected too, and that real indifference at a parting or a reunion is not normal human behaviour. When these moments are handled badly, threat builds up, and under threat partners start to look like caricatures of themselves.

Bedtime and morning

The two most exposed moments of the day, he says, are falling asleep and waking. Going to sleep means leaving everyone and heading into the unknown, and waking brings a moment of disorientation. Children get through both with help, such as a story, a song or someone there in the morning, and adults are no different, whether they admit it or not.

One partner, often a wave, starts a talk about the relationship just as the other is dropping off. It looks like picking a fight, but Tatkin reads it as a reach for contact before the separation of sleep. The island who seems untroubled at night is, in his view, overlooking the same need.

A one-week experiment

Do not take this on trust, he says. Test it for a week.

1. Go to bed together and get up together. Every day.
2. Put each other to bed. Choose a small ritual: read to each other, say a prayer or good wishes for the people you care about, share a look, say goodnight, or have sex. Your partner should be your last contact before sleep.
3. Send each other off. In the morning do something small: a kiss, a hug, a good wish for the day. He calls it a launch.
4. Watch your days. Notice whether your work, your studies or your mood go better. His guess is that they will.

Coming home: reunite first

Coming home is the other daily reunion. Time apart affects you both, he says, whether or not you notice, so he wants the return marked before anything else happens. He offers two forms, and the first is an embrace.

1. Hold each other front to front, close enough that chest and belly touch.
2. Each of you feels for tension in the other's body. You may tap or touch a tense place as a cue.
3. Do not let go until you feel the other person relax. Neither of you decides when you yourself have had enough.

He says it takes a minute or a few. Then get on with your evening and see whether the usual arguments still turn up.

The same applies after a longer absence. He often hears of couples who quarrel on the drive back from the airport: they met, got straight into the car and sat facing forward. In his reading they fought because they never reunited.

Why the eyes matter

Why does facing forward cause trouble? Tatkin says partners are best at steadying each other, which he calls interactive regulation, when they can see each other's eyes. A difficult subject is harder by phone because the face is missing, and worse still by text or email because the voice is gone too.

He gives two reasons, both his own account of how sight works. Only a small central spot of the eye, the fovea, sees fine detail, so you have to look straight at a face to follow it. And the amygdala, the brain's fast alarm, reacts to faces caught at a glance, so talking side by side in a car or on a walk produces false alarms.

This gives the second form of the coming-home reunion: skip the embrace and look into each other's eyes. Each says what they see, for example that the other still looks preoccupied or that their eyes are not soft yet. Carry on until you both agree that the other's eyes are soft and present.

If you have children or pets, he asks you to reunite with each other first. The couple is what everyone else in the house tunes to, and children learn from seeing their parents look after each other. Pairs at opposite ends of arousal, an airplane living with a submarine, need this more often, he says: even each time they cross paths in the house.

The rule of thirds

Tatkin calls this the best predictor he knows of a relationship ending. People are built for pairs, he says, and a primary relationship cannot stand being made secondary. That is the rule of thirds.

A third is anything outside the two of you that competes for what you have. His examples are a task, a job, alcohol or drugs, sex, a child, a pet, in-laws and a best friend.

Thirds are usually neutral. The harm starts when one partner uses a third in a way that pushes the other aside. If your best friend's wishes keep coming before your partner's, your partner will come to dislike that friend, who has done nothing wrong. The same goes for later marriages, he says: they are not sunk by the number of extra people but by the belief that a partner can be sidelined.

So the two of you have to decide who loses when something outside competes. His answer is that it should rarely, if ever, be your partner. If you say you are stuck in the middle between your mother and your partner, he hears a warning. There is no middle, he says: the one who has been left outside is your partner.

Go to your partner first

Thirds also cause trouble at the level of arousal, most often around children. Picture one parent getting heated with a child. The raised voice works like a siren for the whole house, and the other parent feels the urge to rush in.

The usual mistake is to go to the child: to take the child's side, or to overrule the upset parent in front of them. Tatkin says to go to your partner. Do one quick thing that carries no threat, such as a kiss, a word of support or an offer of help, and then leave.

The aim is only to bring your partner back inside the window of tolerance, so that they can think again. Stepping in any harder tells them that you think they cannot cope.

Changing each other's state

That move is one case of a wider skill. Tatkin wants partners to know how to shift each other's state quickly: to calm, to cheer, to enliven. In his practice he asks one partner to make the other feel loved on the spot, so that it shows in the face, and he is often surprised by how many long-married people cannot do it.

The way to check your work is to look, not to ask. When you apologise, you know it has landed when your partner looks relieved. He adds that asking your partner what would make them feel loved is of little use: they often do not know, and when you are in each other's care, finding out is your job.