I don't know, Hanky... the thing about relationships is that you don't necessarily get out of them what you put into them. I always think of relationships as being like a group project where every individual has a particular task or responsibility, and the success of the project depends upon each member of the group putting forth the effort needed so that everyone benefits in the end. When all members contribute their share, or when someone else in the group assists a member who's struggling to complete his or her task, then everyone reaps the good results. But it doesn't always work out that way.
Ideally a marriage should be relatively equal in terms of give and take, but marriages don't always work out that way either. Sometimes that's not either party's fault -- a serious illness or disability can tip the scales to the point where one spouse requires a lot of care but can't contribute much in return. And sometimes one spouse works hard to make changes that will benefit the marriage, but the other spouse refuses to cooperate. There's only so much a person can do to make things better at that point. And then the hard decisions need to be made -- do you love your spouse enough that you're willing to stay in the marriage and resign yourself to the fact that this is as good as it gets? Do your feelings about yourself depend on honoring the commitment to your spouse regardless of the fact that your needs aren't being met? If you stay, can you find some kind of healthy substitute for whatever's missing in your marriage? If you leave, are you prepared for the fallout from friends and family, especially if there's been no actual abuse and you're leaving primarily to find fulfillment elsewhere? What are the chances of finding that fulfillment in another relationship, and are you prepared to start over in terms of finding a place to live. etc?
Lots of questions with no simple answers.