In Upstream, Mary Oliver tells us how all her friends have been shadow companions (more about Upsteam). In seance with powerful minds from the books that kept her company.

I never met any of my friends, of course, in a usual way—they were strangers, and lived only in their writings. But if they were only shadow companions, still they were constant, and powerful, and amazing.

What a wonderful thought! Of never being alone, always surrounding yourself with your shadow companions

A mutual companion of Mary Oliver and myself – Walt Whitman

The moth and the fisheggs are in their place,
The suns I see and the suns I cannot see are in their place,
The palpable is in its place and the impalpable is in its place.