Love is not a manufactured emotion. If you've fallen out of love and its not coming back then perhaps it isn't meant to be. People fall in and out of love all the time, and though it can be difficult, there are not always explanations. Sometimes it just happens. By the same logic, however, sometimes your feelings will just spring up naturally, renewing love where you thought there was none. At the end of the day, the best advice is to follow your gut, be honest with yourself and your partner, and hope for the best.

Summary:
Don't force things.