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Many people feel that their partner has changed. They remember a much sweeter, more considerate person before they were married. They complain about a much less sweet, much less considerate person now.

Has your partner really changed? Or is it your perception that’s changed? Or maybe you’re the one who’s changed? Or maybe it’s some change you two have done together? There are a lot of possibilities. It’s hard to know which it is. Or maybe it’s more than one. Or maybe it’s some external circumstance that’s affected both of you? Or all of the above.

, in his ground-breaking book, Getting the Love You Want, advanced the notion that has stages. The first stage, " ," feels like sweetness and light. People feel wonderful, life is great, and couples bring out the best in each other. The second stage, "The Power Struggle," is not so wonderful. People feel bad, life is difficult, and couples bring out the worst in each other.

Hendrix argued that the power struggle is an inevitable stage in all relationships. The goal of a good marriage is to get out of the power struggle and move toward "Real Love."

In an article to be published next month, a research team at the University of Georgia provided some evidence for this theory. Their article, “ among newlyweds,” will be published in the June issue of Developmental Psychology.

Their research showed measurable and significant changes in the beginning of marriage. The most pronounced change is that husbands and wives become less agreeable.

This fits exactly with Hendrix’s theory.

The Georgia group studied 169 newlywed heterosexual couples for the first 18 months of marriage. They found significant changes in personality — some good, some bad.

All these changes, of course, are “on-the-average.” Not every single person changed in every direction, but there was a substantial average change when considering all the couples together.

On the good side:

1. Husbands became more .

2. Wives became less , , and angry.

Husbands work harder and become more responsible. That makes sense. They take on the attributes of their new role. Wives feel better; they have a more secure, stable and are less vulnerable to various .

But on the not-so-good side:

1. Husbands became less extroverted.

2. Both husbands and wives became less agreeable.

Less makes sense. Husbands spend more time at home, less time socializing.

However, the decrease in is certainly a disappointing finding. Don’t we all wish this wasn’t so?

But it has a ring of truth. Many people have experienced this. The good behavior of courtship tends to fade, old bad habits tend to return. Harville Hendrix would say it’s the inevitable shift from romantic love to the power struggle.

I think it happens as each couple falls out of their "Love Cycle" and gets stuck in their " Cycle." Love cycles build agreeableness; fear cycles build the opposite.

On page 37 of Love Cycles, Fear Cycles, we discuss how fear cycles escalate. That’s part of how people get into in diminishing agreeableness.

This research says it happens to most people. And it starts in the first 18 months.

But that doesn’t mean that you can’t reverse it. You can. You should. And you’ll be glad you did.