Issues found in long-term marriages or relationships such as ineffective communication, issues of respect and boundaries, differences over money, intimacy, work and other issues will not cause an MLC because an MLC is a preexisting 'condition' waiting to be triggered.
Interesting point thetruth. All of those things you name are certainly factors that can cause the breakdown of a marriage. However MLC and the breakdown of a marriage are two totally separate things.
MLC is not a preexisting condition, it is a life stage which some individuals go through, usually between the age of 40 and 60. It can last from two to ten years but the average is around five. It is most likely multifactorial, and perhaps not identical in all persons. The evidence is that in men the trigger may be dropping levels of testosterone in an individual who has a predisposing avoidant coping style. Childhood issues may certainly be at work in the development of the avoidant coping style. In avoidant coping styles a person attempts to hide or run away from problems rather than working through or solving them.
MLC is characterized by the following:
1- A period of withdrawal from family life
2- Depression over the achievement of life goals
3- Engaging in secretive behaviors: hidden telephones, secret phone calls, secret trips.
4- A desperate belief that one needs to start life over, and that in order to do that one must literally run away: abandon ones family, ones work, ones children. In order to do this they must drive their loved ones away.
5- A belief that ones wife is the cause of failure to achieve life goals, and the belief that if one finds the "right person" one will somehow reach those life goals.
6- A tendency to start an affair with an individual who provides flattering attention, and to become infatuated with that person and see them as the solution to all their problems. This affair partner may or may not be "an old flame" or someone who is several decades younger. Once the period of idealizing the affair partner fades, the person in midlife crisis may move on to a second or third partner seeking each time the one who will be the solution.
7- Frequent lying.
8- A sudden event where the person in midlife crisis verbally attacks their spouse and abandons their family. During this event the person in midlife crisis appears to desire to inflict the maximum amount of pain "you are old", "you are wrinkled" "you are no longer useful to me".
9- Failure to guarantee the well being of the family.
10- Engaging in behaviors which remind one of ones youth. This can take many different forms: alcohol, drug use, excessive exercise.
11- Poor money management and financial judgment. A tendency to purchase things one cannot afford to boost ones self esteem - a car, a yacht, a home.
12- Fear of aging, and attempts to dress, act and associate with individuals much younger than ones age. People in MLC tend to look at themselves in the mirror.
13- Problems with anger and poor judgment regarding consequences of ones actions.
14- A generalized lack of empathy for others, and especially for the family.
When these behaviors are engaged in over many years the person in MLC may not just destroy their famly they may destroy their career and their finances. Certainly the above mentioned behaviors may destroy a marriage.
When a normal marriage breaks down ineffective communication, issues of respect and boundaries, differences over money, intimacy, and work can all be factors. The couple can try to discuss these problems and search for a solution or they may argue. They can go to counseling, or if that doesn't work they can separate for a cooling off period, and if that doesn't help they can divorce. However the 14 factors listed above are not characteristics of a normal marital breakdown.