The precious moments were slipping away, but he had forgotten everything that he had meant to say to her and could only helplessly brood on the mystery of their remoteness and their proximity, which seemed to be symbolised by the fact of their sitting so close to each other, and yet being unable to see each other’s faces.
There are no more uses of "proximity" in the book.
Show samples from other sources
They selected the offices for their proximity to D.C. political power.
We like the neighborhood because of its proximity to the University.