You might wonder why tackling relationship/marriage issues from a spiritual perspective is that important. In Neuro-Linguistic Programming (NLP), we have an elegant model depicting the various levels of influence in our lives, called the Neurological Levels, developed by Robert Dilts.

What it means is that any changes that impact your beliefs and values, for instance, will impact your capability, behavior and environment. In other words, the influence effects generally from top to bottom. The least impact is generated from attempting to change your environment, for instance, by controlling your spouse. The most pervasive change comes from dealing with the situation from a spiritual perspective.
Example:
Problem:
Spouse says that he/she has found somebody else and wants to leave you and tells you the classic "I love you but I am not in love with you.".
Working on Your Environment
Try to control, manipulate, persuade or plead your spouse to come back to you.
Working on Your Behavior
Stop criticizing and controlling your spouse, for instance. Lots of relationship self help advice tell you not to be jealous, to be independent as opposed to being co-dependent, to communicate your feelings etc. It all sounded great but I was still clueless as to how exactly to go about doing it. In times of stress, as in the midst of a heated argument, for example, somehow these well-meaning advice slipped through my mind. Although I am a very determined person, my will power alone was not enough to change my behavior.
Working on Your Capability
Learn skills that teach you to behave in certain empowering ways, so that you will not resort to behaviors that cause a rift in the relationship.
Working on Your Belief
Examine your belief system – what disempowering beliefs do you have about yourself and relationships? For instance, do you believe that you are not good enough? Do you believe that all men cheat? Beliefs affect how you relate to your spouse.
Working on Your Identity
How do you see yourself? Do you see yourself as a loving person, worthy of love? For instance, if you don’t see yourself as a lovable person, and give yourself that love and respect, chances are your spouse may not either.
Working at Spiritual Altitude
Identify the spiritual lessons that you need to learn from the situation that you are facing, and you act from love, instead of fear. Identify and break repeating patterns of acting as though you are undeserving of love, energetically. This will not only change your relationship or marriage for good, but will also positively influence all other areas of your life, as a pleasant side effect. It will stop your unconscious patterns for good, at the root causal level. What it means is that you will stop unconsciously “inviting” undesired behavior in your relationships, stop feeling that you are not good enough (ego) and start respecting and honoring the spiritual self within you (Higher Self). The changes that take place are from the level of your core essence, your soul, from within.
Also, you learn to relate to your spouse as your Higher Self, as opposed to, from the level of your ego. Your marriage stops becoming a battle of two egos, competing to be right, appreciated and valued. You energetically change the direction of your marriage, by deliberately designing your own reality. If you are working on your marriage alone, you don't even have to involve your spouse physically at this level.
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Granted not all problems may need a spiritual solution. Some problems may even respond to external changes. Here, I am focusing more on issues that have resisted previous attempts at healing at the environment/behavioral level. The most effective combination would be, tackling the problem both from a behavioral and spiritual perspective, with a greater emphasis on the latter.
Credits:
Richard Bandler
Robert Dilts
An Relationship River Analogy:

The spirit aspect influences the mind and the mind influences the body. Think of it as a river, the spirit being the upstream aspect. If your upstream is muddy, then no matter how you try to clean your downstream, it will get muddy eventually. This applies to saving relationships and marriages as much as any other related issue that you may be working on, eg self-esteem.