Just like a beautiful garden, a relationship requires nurturing. When the people in the relationship fail to maintain it, the relationship will wither and eventually die. It is important to continue dating and making each other feel special. This gives both partners a chance to see each other in the same way as when they first decided to make a commitment. It brings light and life back into a relationship that may be withering away.
Taking a long term partner out for dinner is a good way to nurture a relationship. Making it a very special dinner takes time and effort, but it pays off in the long run. Don't just go to the regular pub or restaurant. Make a change and go to a new place where neither has been before. Add an unusual entertainment if the restaurant is not overly exotic or special in some way. Making the investment of dinner for two will keep the relationship healthy.