I think most posters here really believe that they are supposed to make the marriage work until death. Once they commit to the marriage they are stuck with each other. Once you are stuck with a person you make the best of the siuation.
Your logic works fine in a friendship .... "why go to dinner if it is only out of obligation" or it works fine on the job "why stay at the job if it is not working for you"
However, does either party have a right to split when they become bored with each other? I think that the whole premise of most posters here is that once you are in the marriage, you are beyond picking and choosing. Sometimes the ONLY thing that keeps the marriage going is the extent to which each party believes in obligations and commitments. Most posters here, even the divorced ones, I am sure, feel that they are sinning against God if they simply toss the relationship aside when it no longer makes them happy. Most divorced people struggle mightily with God's stated will and the practical hardships they are in.
If your view of marriage is the same as your view of sex, then when one becomes tired of their partner they simply move on. No morality issues, just get out and find someone else to make you happier.
Your ideas only make sense to me in a world where marriages are not morally binding.