You are wrong. Love doesn't waver. You can be upset at someone or disappointed or even angry, but if you really love someone, that love doesn't change, ever.
Answer me this. Can you fall in love? If so then you can fall out of love. Feelings are fickle.
A good marriage demands constant work and nurturing. In the beginning when the feeling of love is strong in both partners this nurturing is all but automatic. But as the years go by when the feeling fades but the decision remains this nurturing becomes work. When his habit of leaving his socks on the bathroom doorknob even though you've asked him time and time and time again finally gets to you, when you can't stand his incessant whistling one second more, when he's ticked you off so totally that the last thought that would ever enter your mind is to do something nice for him, THAT is when you have to work on nurturing the marriage. And that is when the work pays off the greatest rewards.
Mankind is a failed creation. We are sinful in all our ways and that nature in our bodies willonly be overcome in the next world. Until then we have to put up with each other. We are, by nature, unlovable. And that is why love is work.