In Golden Age mysteries, it is customary to have a courting young couple--so much so in Ngaio Marsh's mysteries that her courting couples (with the exception of Peregrine and Emily) tend to blur together.
Agatha Christie was exceptional, in part because she had the capacity to imagine different types of relationships. Still, the custom is such a strong one that several mystery writers remark wryly on it.
The custom has continued into the present day. It is apparent in Ellis Peters' books. Nearly all of Ellis Peters' books have a courting couple, helped quite often by Cadfael. However, one major difference to other courting couples in mysteries is that the Peters couple is almost always directly connected to the problem: the young squire who wants to marry his lord's fiancée; the young woman who is courted by a possible sociopath; the young monk who realizes he doesn't really want to be a monk after all and stays in Wales.
A non-consummated, non-young relationship is Cadfael & Sister Magdalen (formerly Avice of Thornbury) who meet in The Leper of Saint Giles. They both came to the religious life after a life in the world, and they tackled worldly pursuits with eyes wide open. They took on their religious avocations in much the same way. They are kindly, pragmatic, and natural leaders, though Cadfael sticks to a more independent style of leadership.
The book and television series both do a good job implying a natural bond between the two.
Ellis Peters's "modern" mysteries (they take place from the 1950s to 1970s), give readers George and Bunty: the solid, mutually respectful relationship of two people with distinct personalities, interests, and experiences.
