Hmm...it depends. Marriage is the only place where I'm willing to ride a whole lot of waves of change at this point.
If I realize I'm not in love with someone anymore, I would first assess why and if there is anything that can be done about it.
I have to say that I don't believe that being IN LOVE is as important as LOVING somebody. You can fall in love with anybody, but you CHOOSE to love the person you are with. So, I guess the bigger question was, does this person/relationship matter enough to me to continue choosing to love them? Because over the course of a marriage, you are not going to be in love all the time. I think it's wise to learn the meaning of loving a person with whom you are not in love.