There are unique reasons for their unusual relationship, but even putting those aside, they are onto something. Walking frees the soul, and if one soul is strolling with another, confidences are easily shared.
It may be the same process that loosens thoughts in the solitary walker, or it may be that the sheer mechanics of it means you are looking ahead and not at each other. Whatever the explanation, walking invites intimacy, as it did for this couple:
Nobody ever bothered us. ... We were often so deep in our conversations that we often didn't notice our surroundings. Miraculously, the streets kept us safe and the people let us be. ... We were devoted to each other.