on the topic of what can go wrong in marriages and how to keep it from happening... Ravi Zacharias has this to say:
First and foremost, do not even flirt with the idea that there may have been somebody better out there or someone else with whom you may connect better. Infidelities are not always physical. Emotional vagaries of the mind can be equally dangerous to the health of one's marriage. Mind games can bring bigger losses than imagined and should be stifled early. Receiving the partner as a gift from God, "warts and all," is a commitment with which one begins. The hard thing about this is that both of you need to deeply believe this. One person alone on the path of unconditional love can find it terribly exhausting.-- from I, Isaac, Take Thee, Rebekah (ch 7 / p. 137-9)
A sincere soul-searching is the most important step when trouble looms large. Affairs often begin because one person finds someone else he or she relates to better and with whom he or she experiences more intimacy or warmth, without all the burdens of carrying a family. It may just be that many marriages break up after years of raising a family because the concerns that have been shared after half a lifetime of bearing one another's burdens are too big to carry any longer. But this is where we have to step back and realize what love and marriage are all about. Marriage brings together not just a man and his wife but their children and their struggles. To suddenly drop the partner who has carried that load with you along life's journey for all these years for someone with no strings or worries attached is cruel. Marriage is not a commercial enterprise in which you replace a car you have tired of with another one. The truth is that the new car will lose its appeal, too, to say nothing about yourself. Someone has said that a man owes his success to his first wife, and he owes his second wife to his success.
From its very inception, kill the thought that there is somebody better out there, with arms wide open, just waiting to bring you perfect happiness. Freedom from joint responsibilities and concerns is always idealized in the short term but is never realized. The greater the degree of immersion in another's life, the greater is the "pain" of living. That is just the way it is. The greater the involvement in another's life, the greater is the demand for sacrifice. We are not here to be coddled and made to feel better. There is no perfect person out there, and "better" can be a very misleading term.