You cannot simply just fall out of love with a person. If you have, perhaps you don't understand what love truly is. Love is an action--it is a choice. Everyday you make a choice. You either choose to think of your spouse and choose to show them, or you don't. It's that simple really.
Sure, love can die. Just like any living, growing thing, love can die without proper nourishment. Laziness will keep a person from continually caring for the seed of love they have planted with another person. Neglect, as a product of laziness, is possibly the saddest method of killing love. What a tragedy when two people love each other, but sit by and do nothing to nourish their love until it is too late!
Selfishness and pride are also the weeds that will overtake the blossoms of the love you once enjoyed. Is it really that hard to be kind and thoughtful toward your spouse? Is it really that difficult to admit the ways that you are poisoning and depriving the soil of any nutrients that keep your love from growing? You may think that it is better to keep your pride at the cost of love. You may think you can just start over, but I guarantee you will never find something better. It will take work, humility, and unselfishness to grow new love. You obviously have yet to acquire those traits if you just allowed yourself to "fall out of love" in your last relationship so you are already set up for failure. And if you ever do figure out how to truly be in a relationship, you will regret that you didn't put the work into that first love because new love will never be as beautiful and it will require much more work to maintain.
So, let's stop with the lie that love just dies. That justification might make you feel better for a moment, but let's get real. You have some work to do. Choose to love your spouse every day. Choose to find ways to let them know you love them. Choose to be the person you should be for your love.