SO THE Duke and Duchess of York have formally separated. Yet pictures of them with their daughters suggest they are striving to be good friends. In the same week, the camera catches a wistful look from Prince William as his parents kiss goodbye after his school sports day. But whatever the reason for such public reconciliation, can the royal couples, or any separated couple, truly be friends again?

When a childless marriage ends, a clean break is possible. But when children are involved, the belief that everything is over is a dangerous fiction. And it can be just as dangerous to hope to become friends again. An uncomplicated friendship with the person you wanted to be rid of is not a realistic aim.

The fact that there are children also puts paid to the belief that divorce means the end of the relationship - which can come as a rude shock. Many people would adjust far better to divorce if they saw it as leading into a different, longer process of attenuation and change in a necessarily continuing relationship.

A year after her divorce a woman I know moaned recently, 'How much longer am I going to have to hear his stupid, braying voice over the phone?' Her ex-husband was calling to make tortuous arrangements over the children. The answer to her question is, 'As long as you have children, with decreasing frequency and intensity after they leave home, except again at family occasions.' Anyone not prepared to accept this will be angry and frustrated.

Divorcing couples often do not recognise the ways in which they will still be tied to each other. Anger, bitterness and resentment are negative but strong ties, and keep couples in a marriage even when it is over. Divorce should be a long-term process, an emotional distancing, so that the actions - good or bad - of either partner make little difference.

As for the expectation of 'friendship', this is a minefield. Over the years, many couples in my practice at the point of divorcing have said, 'He/she used to be my best friend. Why can't we be friends?' Or, 'We're good friends but we just can't get along.' I think they are stretching the definition of 'friends'.

Let's be clear - divorce is serious. It has many consequences, especially if there are children. Divorce means a breakdown of a friendship, 'no longer being able to get along' in some fundamental way. Why should your ex-spouse be any different, with you or the children, just because you have stopped being married? If she was critical and curt, why should she suddenly become encouraging and effusive? If he gave the children junk food before, why should he act differently now?

The main difference is that more of these 'objectionable' qualities are focused, undiluted, on the children. As the ex- spouse, such qualities will still get to you. The difference is that after divorce you are more powerless, and will feel even angrier.

Divorce does not give the space for love or friendship to grow. It gives the space for people to grow apart. Friendship does not thrive on these grounds. It certainly doesn't help the children to adjust.

A woman who had moved in with her lover continued to visit her ex-husband and children in the family home daily, even offering them temporary accommodation. The children were confused. 'If you and Mum get on so well,' the 10-year-old asked her father, 'why did you get divorced?'

Research shows children rarely give up hope that their parents will be reunited. They believe that with will, luck - maybe magic - parents will love each other again, and they will all live happily ever after.

Children wish to be with both parents, in a conflict-free, loving home. They can adjust to divorce, of course, and in many cases do so very well, in time, in the right conditions. But one condition is clarity: being close post-divorce is confusing and holds out false hope. Such involvement also keeps people stuck in a kind of no-man's-land in which there is no marriage, nor any new lease on life.

Couples used to stay together 'for the sake of the children'. One in two marriages in Britain fails - the highest divorce rate in Europe - and so for many people the real question needs to be 'now that we are divorced, in what way do we continue some sort of relationship, for the sake of the children?'

Research points out some of the ways. Clarity is a key. Reducing overt conflict is another. Not putting the child in the middle of relationship negotiations or maneouvres is a third. Showing the children that you respect their love for, and relationship with, their other parent is also crucial. All of these are often undermined by expecting that, after divorce, you will never have to deal with that person again, or that that person will magically be transformed into a reasonable being, or that in time you will regain an easy relationship.

The post-divorce relationship is not a marriage. At best it is a fragile but necessarily dedicated alliance. It is not friendship.

The author is a psychotherapist and affiliated lecturer at Cambridge University. She is co-author of 'Sexual Arrangements: marriage, monogamy and affairs', published by Mandarin.

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