I have seen on many occasions where a husband and wife may have an issue. And both spouses confide in some one else outside the marriage. This has both good and bad consequences.
First, when you share your unhappiness with some one else, what they hear is your side of the story, and your side only. Even though your feelings about your spouse are valid, they are none the less, biased. Therefore, the advise that they are giving to you is based just on your side of the story, and not the parts that you may have accidentally left out, and certainly not the other spouses side. This may complicate a marriage even more.
Second, because you are very dear to your family and friends they can’t bear to see you in pain. Therefore they will steer you in the direction of what they think is the quickest escape from your emotional torture. They may try to convince themselves and you that since your spouse is the problem, you should get rid of him/her. They may say things like, "You don’t deserve this; why don’t you get out." They want to see an end to your unhappiness.
Finally, your confidant can only advise you to the extent of their success or failure in their personal relationship. Their advise is based on how they view life. Which may or may not add another bias to your situation.
One thing I would like to say about confidants is that after you have made whatever decision you make about your relationship, you are the one who have to live with that decision. Your friend or family member may be there for you, but you are the only one who will be feeling the pain.
I am not saying that you should not discuss your marital issues with some one else sometimes. On the contrary, what I am saying is that in listening to their advice, just remember that, a) their opinion is most likely a bias one, b) It will make them feel better if you are not so unhappy, thus making their advise also self-serving c) They can only advise you to the extent of their personal relationships.