How marriages get into trouble
Expectable marriage patterns
In the large majority of cases, the early years of a marriage are the happiest. Marriage happiness ratings tend to be highest during the first one or two years of marriage, and then drop to lower levels. A variety of factors, most prominently the introduction of children to the family, place considerable demand on the marriage which are difficult to negotiate. Parenting takes a toll on the ways that partners tend to experience each other. Marriage satisfaction levels off as children leave the home, but frequently the partners never recover the intensity of feeling they originally had for each other. Thereafter, the marriage may function quite well and both partners may be quite content, but some portion of the passion that was originally present has burned off.
It certainly isn't fair that passion tends to die down over time, but it is an observable fact. It has been suggested that we have perhaps evolved to only stay passionate with a partner for a time-limited period (just long enough to get pregnant and raise a child through the most sensitive parts of early childhood), but this remains speculation. Whatever the cause, among the many challenges that spouses face in keeping their marriage strong is finding ways to keep some passion alive, and adjusting to the fact that as familiarity increases, some passion will likely leave the marriage and that this is a normal process. Partners who seriously fail at these tasks can drift apart emotionally and/or fall pray to temptations such as extramarital affairs.
If a picture of marriage satisfaction over time looks like a downward sloping curve, a picture of how marriage problems look through time resembles an arch. Few problems are recognized in the early stages of marriage. Marriage problems tend to rise in the middle years of marriage, probably in response to family obligations including raising children, caring for elderly parents and the like. Finally, reports of marriage problems drop off as care giving responsibilities decline.
While long term patterns of satisfaction and complaint tend to occur as described above, what is happening at any given moment for any given couple is far more variable. Family, friends, employment and country make continual demands on married people. There is a certain normal waxing and waning of closeness that usually occurs between the partners as they negotiate these varying demands. At some times the relationship will be most important; at other times, work or military service, or parenting will seem more important. Normal relationships, (unlike the fantasy ones featured in movies) do move between intimacy and detachment. This is important to keep in mind so as not to panic when evaluating your feelings for your own spouse. Ocassionally feeling distant or detached from your spouse doesn't mean that a real marriage problem exists, so long as your detachment doesn't persist and so long that on average your marriage remains your first priority.
Some marriages fail. Given the long-term predictable declines in marriage satisfaction and the predictable rise in marriage complaints that tends to occur in the average marriage, today's high divorce rates are perhaps not shocking. In recent years in America, approximately 50% of all marriages have tended to end in divorce. Many divorced people remarry, but the statistics for divorces among remarried people are even worse, with over 50% of those marriages failing. Conservative critics get upset about the high divorce rate and look nostalgically backwards to earlier times when the divorce rates were lower. What such critics don't tend to focus on, however, is that while divorce rates were lower in past decades, divorces were also much harder to obtain. There is no reason to believe that just because prior century couples stayed together more often that their marriages were any more functional or happy than are those of today's divorcing couples.
Divorce is a highly public and obvious formal sign of marriage failure. Depending on how you understand and define marriage, however, there are other ways that marriages can die. Modern marriage is both a legal and social arrangement as well as an intimate and emotional partnership. A formal marriage can persist for years after the emotional and intimate parts of it have perished. This sort of arrangement might be a fine agreement if both partners wish it, but an unfortunate fate if one partner does not but for whatever reason won't or can't muster the will to leave.