Be alert when circumstances change. Whether it is the arrival of a baby, a move to a new house, a change of job or the loss of a friend, basically any change - also the good ones - can cause disturbances in the marital balance.
A person, whose emotional needs are no longer met by his or her partner, may turn to the children, parents or in-laws for gratification. A spouse should take this as a warning sign. Eventually, he or she might turn to another lover as well.
Putting blame on one's partner is one of the easiest things to do. Subsequently, giving in to the urge to 'get back at' a partner tilts a marriage even further out of balance.
The right thing to do, but far more difficult, is to discover what one oneself could and should change.
Breakdowns of marriages don't happen because of differences. They happen because the couple can't handle those differences.