Ok...I am going to sound like the 'old man' here now but for what its worth...
Having been married for over twenty years, I can say that as a couple, you both go through times when you have these feelings. How you handle them is what makes the difference between a good relationship or not.
The biggest thing to remember is you BOTH have to be HONEST and straight forward with each other. You also both have to WANT to save or continue with your relationship.
That said...if you are asking questions about your relatinship...you really need to talk to your significant other. You both need to honestly and straight-forwardly discuss yoiur feelings with each other. After that...if you still feel that you have deep questions about your situation...then cut loose. Don't hesitate after a honest disscussion. To do so will just bring pain and anguish to something that probably would not have survived anyway.
Just my two cents worth. I hope that you find what you are looking for sheath. Happiness is important in one's life.