Most books about love are about its beginning. These are about its middle — the long stretch where the chemistry has leveled out and what remains is a set of choices, habits, and repairs. That is the more interesting subject. What makes love last is not mystery or intensity. It is something quieter and more demanding: the willingness to be known, the practice of repair, the capacity to stay curious about someone you think you already understand. These books cover that territory without flinching.