There is nothing coincidental about relationships lasting forever. It's called work. Relationships, marriages, whatever your commitment is to another human being, requires WORK.
While the romantic nature of fairy tales does eventually fall by the way side as "real life" intervenes (jobs, bills, kids), the true test of love is if you still feel passion for one another IN SPITE of the loss of the fairy tale. And not necessarily physical passion, although I believe that's critical, but passion for the life you lead together.
I do agree with Capo's advice to let yourself experience the pain and let it out in a healthy way, Whisper. Take those long walks. Don't be afraid to grieve. And don't dwell on the past.