There are some men, who don't want to be with just one woman for sexual reasons. There are some men who feel they have outgrown their wife. This happens often where the wife is at home with the kids and he finds that he is no longer attracted to her and would rather seek the attention of a work colleague. This is an awful situation, but sadly, it is more common than you would care to imagine.
It is not the easiest thing in the world for two people to live with each other and go on and forge a happy life together. There are many couples that have done this and have had wonderful marriages. Sadly, there are many couples that have tried (and tried hard in some instances) but have failed and the marriage has ended.
If you are having marriage problems and don't want to wind up in the divorce courts, you should take steps to make sure that you don't find yourself ending a relationship that could have been saved. Why men leave marriages is because they haven't been able to fix what was wrong in the marriage. This is where the right help can enable you to determine why the marriage struggled and what is needed to overcome your problems. Many relationships end because the parties simply don't work hard enough on the root cause of the problem.
In cases where the problem is detected and a plan put in place to overcome the problem, couples are well placed to move forward especially if their love is strong. It is a great tragedy that many good marriages have fallen by the way side when they should not have.
In summary, there are two types of men - those that are contented being in a monogamous relationship and those that aren't. Those that aren't are constantly restless and prone to having affairs. They generally will struggle to commit to just one person and will have trouble remaining married. They really do have problems and need help to work out what they can do to be more contented in their married life. If you are in this position and you have a fair idea why men leave marriages, the quicker you seek this help the better.