A family friend said something funny but all too true to me last week: "Once you get married, it's like you never get to see your husband. That's why it's for time and all eternity; that's the only time you'll ever see them." Her husband is currently the stake president =).
I think this is what people in successful marriages understand: the goal isn't for the marriage to make us happy, or for our spouse to make us happy. The marriage unites us in a common journey toward a greater goal--eternal life. It's the toil and the work in that cause that will make us happy. A good quote from SWK:
"Divine love is not like that association of the world which is misnamed love, but which is mostly physical attraction. … The love of which the Lord speaks is not only physical attraction, but also faith, confidence, understanding, and partnership. It is devotion and companionship, parenthood, common ideals and standards. It is cleanliness of life and sacrifice and unselfishness. This kind of love never tires nor wanes. It lives on through sickness and sorrow, through prosperity and privation, through accomplishment and disappointment, through time and eternity” (The Teachings of Spencer W. Kimball, 1982, 248).