The Ten Commandments in the Bible were never meant to be a Mantra to cause ill-rest and religous wars, but rather a useful guideline as to have a happy life.  The Secret is based on the loaves and fishes story in the Bible, and it is true that what you focus on actually expands.

Depression can happen when your basic needs are not being met, and love is missing from your life.  Humans are mean to live in a world of love like the Garden of Eden, and to express our sexuality as a reward for giving our love to each other.

When we meet someone, we notice something about them that we like, and if we give the thing we like some energy we will find we start to notice more good things about them (we are actually compiling a list in our mind of things we admire about them), and if the list grows quickly, we can fall head over heels in love with them.  While we are focused on the good points about them, our eyes don't notice anything bad about them (love is blind).

A marriage will sail along in calm waters as long as we continue to count the blessings of the marriage, but sometimes spouses can have mid-life crisis and start to feel they are becoming less attractive and the rewards of marriage are not what they expected.  

A marriage should be a partnership of helping each other's needs get met, but husbands and wives can stop talking to each other through a mid-life crisis - no longer sharing the insecrities they are feeling.   A spouse may talk to her friends, but not her husband, so a rift occurs and the couple grow apart.

A relationship can be rescued if both parties agree to start counting the Blessings of the marriage again.  This starts the snowball rolling to bring back the love and emotional closeness that once existed.

Adultery or pornography are enjoyed by more than 50% of modern couples according to surveys, and not necessary grounds for urgent divorce - more of a starting pont to re-negotiate the future direction of a marriage.  See it like a business in deep trouble, that needs a new sense of direction.    Everyone gets hurt by divorce.

Before very long, both spouses are counting up the things that are wrong with the marriage, and like a snowball as Rhonda says in the Secret,  the list of wrongs grow faster and faster until there is no marriage left.