When a couple finds their relationship has stagnated after a few years or decades, they have to choose whether to end it or learn to be together again. Both of them must work at it, or the relationship will ultimately fail. Each of them will need to rediscover what they cherished in their partner when they got together, but they must also find out what they cherish about their own life as part of the process. People change as they age, so what suited them at first might be something neither of them wants any longer.
Optimism is often said to be something for the young, but there are people who manage to avoid becoming cynical as they age. For couples who are redefining their relationship, optimism is a key element. They need to be open to the changes in their own wants and needs as well as those of their partner, and they have to be willing to use the past as only a guide instead of a tool for the future. Each of them has to be in this frame of mind for their relationship to continue.
If one partner loved to dance when they first got together, it might not be possible for them to enjoy it as an older person. Their taste in activities might have changed, or their physical debilities might make it impossible for them to do the same things. A partner who recognizes these conditions exist has a better chance of helping to reform the relationship, and they should also look at the changes life has made in them so they can share them with their partner.
Life does many things to change people as they age, and physical limitations are only part of it. Maturity makes people look at life in a different light than youth, so acknowledging these changes is part of what will help the relationship survive.