Nathaniel Branden is in love with love.

Romantic love, passionate love -- that-deep "spiritual, emotional, sexual attachment between a man and a woman."

Love that entails "intimacy" and "vulnerability" and "an intense commitment."

Love that, when frustrated, can generate "the most unutterable suffering," but which can also bring "the most profound ecstasy."

Love that, even in this day of growing divorce rates, can endure a lifetime.

"Since I was a boy, 10 years old," says Branden, a Beverly Hills psychologist and author just turned 50, "it never made sense to me that people are unhappy as they obviously are. 'This cannot be the nature of life,' I told myself.

"Wanting to know why," he says, "is one reason for motivating me into studying psychology." Which in turn led him to ask professionally:

"What the hell is going on between men and women when they fall in love?And why are the results so often calamitous?" It is a "burning question," he says, largely unaddressed by psychology. Sex, yes, but not love.

For Branden himself, who has just written "The Psychology of Love" (Tarcher, 210 pages, $10) -- which could make him "The Love Doctor" -- love has been an "experience, an incredible adventure."

A youthful marriage, at 22, ended in divorce, but a second marriage brought an "excitement" into his life for 15 years "that seemed almost magically and irresistibly self-rejuvenating," before the death of his wife three years ago in a drowning accident. He has just remarried and "a new journey begins.

Branden's book, based in part on responses from "self-esteem" workshopsps he has given around the country and on 25 years of practice as a psychotherapist and marriage counselor, is a provocative one. Among the myths he challenges:

Children help a marriage. "It's the joke of the century," says Branden, who has no children, though his wife has two of adult age. "It takes a great deal of effort to protect love for a spouse against the demands of the children."

Studies reveal, he writes, "that friction between couples tends to increase with the birth of the first child." The relationship only begins to improve "when the last child leaves home."

Extramarital affairs result from sexual frustration. To the contrary, he says, "Many persons engage in outside relationships with partners they perceive as less attractive and less sexually exciting than their mate." What is often involved "is a powerful desire for novelty and variety."

You can, he says, "love somebody and have a desire for someone else." But "If you're deeply in love, I think it's normal to want an exclusive relationship."

Many people in their 20s and 30s favor open relationships, but as they grow older, says Branden, "The wheel turns. They want exclusivity again -- the stability of one relationship."

It takes "wisdom of handling" for a couple to cope with a spouse's infidelity. An affair "doesn't have to end the relationship. There are too many reasons it can happen and not reflect on that relationship."

He suggests a couple discuss how they would handle such a situation before it happens.

Falling in love and staying there is not easy, concedes Branden, but most people "spend more time planning their vacation than they do examining how to make their marriage work."

It requires "more of us, in terms of our personal evolution and maturity, than we generally appreciate."

Given all the psychological problems people bring to a relationship, he writes, "given their doubts, their fears, their insecurities, their weak and uncertain self-esteem . . . it is not astonishing that most romantic relationships end disappointingly."

Still -- to lighten the hearts of June brides and grooms -- many do succeed. In these relationships, Branden has found, the couples generally share:

A healthy self-esteem: "The first love affair we have to consummate is with ourselves. If you don't feel lovable to yourself, you'll sabotage at some time any love relationship you enter."

A deep belief that you have a right to be happy: "Many people do not." In his workshops, the "overwhelming majority" admit they "start getting anxious when they've been happy for a length of time." For example, he writes, the child of unhappily married parents may internalize a "subtle message from Mother or Father to the effect, 'You are not to be any happier in your marriage than I was in mine.'"

When happiness triggers anxiety, he advises, allow that feeling and watch it, but do not let it manipulate you into behaving self-destructively. "Across time, we can build a tolerance for happiness . . . then romantic love is allowed to grow."

Autonomy: We must have "self-direction, self-reliance, self-responsibility." Love cannot grow, says Branden, if "I believe my partner was put on earth just to satisfy my needs" or "I can't tolerate any real degree of aloneness. That leads to clinging, clutching, suffocation.

"Romantic love is for grown-ups; it is not for children."

Romantic reality: "the ability to see with a fair degree of clarity whom we've chosen as a partner -- the short-comings as well as the virtues." It's immature, says Branden, "to use that person as the springboard for our fantasies, to fall in love and marry and then get upset when we realize that person is not the fantasy. How can you love something that you don't know and understand?"

Courage: "Falling in love can be terrifying. There's always the possibility of loss, of something going wrong -- at the worst, death." Many people deny their fear, says Branden, and this can jeopardize a relationship.

"They don't let themselves know how badly they'd feel if they lost their partner." Then when something intrudes, "They don't fight as hard to save the relationship. They're too busy denying they will be upset."

An abstract perspective: People should realize that "in every relationship, there are times when things don't run smoothly, a time when we disagree. Only children believe you fall in love and move from glory to glory."

Branden's wife, he says, once told him: "I have seen you very, very angry. But I've never not seen that look in your eyes that you're in love with me."

Mutual admiration: "Sexual passion alone cannot sustain a couple across a lifetime. Only admiration can do that." For many, it is frightening to ask, "Do I admire my partner?" That "is to risk discovering that I may be bound to him or her more through dependency than admiration, more through immaturity or fear, or convenience than genuine esteem."

Sexual integration: "lots of people," says Branden, pointing to one side, "grow up with their values here" and, pointing to the other side, "their sexual psychology over here." They are "alienated from their own sexuality" -- perhaps by "antisexual messages absorbed in childhood from parents" -- which can bring about a bewildering disintegration of love.

Recognition of the inevitablity of change: Our "chaotic, rapidly changing world is awfully frightening. We look at an intimate relationship to be a fortress against the world. At home, we dream here at last is a kind of sanctuary.

"But this can make us scared of change. A change in a partner -- the wife wants to go back to school, the husband wants to change careers at 40 or 50 -- is threatening." Partners "try to freeze what they've got, and very often the partner makes him or herself the enemy."

Instead of being an enemy, try, advises Branden, to "be a friend. See what our partners are grasping for. It can be a very powerful bond between us."

If, despite all this, a marriage fails -- a time can come when a person's needs are different" -- Branden offers this consolation: It is "an error to assume that a marriage is invalid if it does not last forever. The value of a marriage is to be gauged by the joy it affords, not by its longevity."

It may have been "a great experience that one is glad to have lived."