It's a cliché because it's true: sometimes some time apart can save a marriage. It seems counterintuitive, but trial separation can actually be a really proactive step toward healing and saving a troubled marriage. The most important thing you can do for a relationship is to know when the stress and anxiety of everyday life together is getting in the way of communication, happiness, or even your ability to cope. Time apart can help you to regain perspective and allow what time you do have together to be honest, productive, and constructive.
The dynamic of a relationship can change in many ways over the years, and when it changes, perception can become so clouded, and so much stress can result, that time apart can be the only way to save the relationship. Profound life changes can result from a major illness in the family, a career loss or change, or when either of these things creates profound financial stress. Sometimes it's good to figure these things out for yourself, and in the face of the kind of confusion these feelings can create, distance might be the best medicine.
Separating for a prearranged period of time can give perspective on the reasons you fell in love with your spouse to begin with, remind you that you feel more happy and fulfilled when your together, and let you remember the good times without being reminded of the difficulties on a daily basis.
The most difficult part of this process is deciding when things are dire enough that a trial separation would be the best thing for the marriage and do more potential good than harm. Each couple will come to this realization at different times and after differing levels of crisis and stress. Generally, however, there are a few points in a relationship that will signal that a separation is best for most couples.
If you are constantly preoccupied with the thought of leaving, this is no small fantasy. This is a major red flag, and certainly a time when a trial separation should be seriously considered. But let's think about why you're preoccupied with leaving. Certainly these thoughts would occur regularly is the bad times outnumbered the good. This is also a red flag and a good time to rethink things. When there is more pain and sadness than happiness, then there is little reason to stay. A major personal reinvention is in order. Also, when the same serious issues come up in arguments and they never seem to resolve themselves. This may be a time when distance can provide perspective and a little bit of time for personal reflection.
But remember, a trial separation is a serious, last ditch effort to affect change in a relationship. It is not to be taken lightly, as a separation can remind you of the good times and bring you back together with your spouse, but it can also - and perhaps more easily - show you that a divorce is the best route to take.