Marriages don't fall apart overnight; people go through a process in order to arrive at their desire to divorce. In some minority of cases, the decision to divorce is made quickly, perhaps as the result of an affair, or an instance of abuse. More often, however, people contemplating divorce endure a period of ambivalence during which the pros and cons of staying or leaving the relationship are debated.
The process of being ambivalent as to whether to leave or stay in a marriage is not necessarily orderly or linear, and there is no set timetable for how long it will last. In fact, ambivalence towards marriage can last indefinitely. Spouses with conflicting goals or values might initially contemplate divorce only to later back away from that idea and attempt to make a compromise work so as to preserve their union. If compromise proves sustainable and successful and both spouses feel good about it, the marriage peace can last. Alternatively, if attempts at compromise are not sustainable (if compromise would lead one or the other partner to compromise too much of what is precious to them) then conflict (and ambivalence towards the marriage) will surely emerge again. Ambivalence indicates a problem in the marriage and is a good indication that marital counseling is in order but it does not necessarily indicate whether that problem can be overcome or not.
Core value conflicts between partners may develop over time as partners mature, or they may have been present in hidden form from the beginning of the relationship. Whatever their origin, mismatched values and beliefs can become an intractable problem for married partners; There are things that partners can compromise on and things they can't yield on without compromising themselves. When partners are unable to arrive at an acceptable mutual compromise, they must either split or figure out how to feel okay in spite of not being able to get what they want. As neither of these 'solutions' are enjoyable, it is fairly common that people retreat from them psychologically and remain ambivalent instead.
People often experience ambivalence as a pressing problem that they cannot solve, and as a painful sense of stuckness. While there are all too many cases where ambivalence ends up being a negative experience from which people have difficulty exiting, ambivalence can sometimes be a good thing as well. Ambivalence might be all that keeps one partner from quickly separating from his or her spouse and ending a perfectly good relationship when he or she is under the influence of an infatuating affair. The laws governing divorce in most states seem geared to support this type of 'take-your-time' ambivalence when they require a period of time to pass between when a couple files for divorce and when that divorce is granted. Sometimes the impulse to flee a relationship is founded, and sometimes it isn't. In its positive aspect, ambivalence slows down the decision making process so that better decisions can be reached.