Yesterday it came to me. The source did involve C.S. Lewis, but it's a memoir by his brother, a preface to a volume of C.S.'s letters. W.H's voice is uncannily like his brother's, with whom he was indeed tightly bound from birth until C.S.'s death at 63 in 1963, sharing a household through most of their adult lives. As children, they were both dreamy boys who lived almost entirely in worlds of their imagining, which they shared, drawing and writing together, in the precious hours when both were home. They shared intense traumas: yearly separations from the earliest age at separate boarding schools, which in Jack's case were barbaric bastions of sadism; and the death of their mother from cancer when Jack was 8. Here's W.H. on Jack's last weeks:
Viewed through the prism of the immortal and homely longings expressed in CSL's work, this is almost unbearably poignant. In fact it occurs to me that I was not entirely wrong in first sifting those writings to locate this scene. In Till We Have Faces, a reimagining of the Cupid and Psyche myth that in my view is his best book, the narrator's unsated life's longing is reunion with the adored sister, Psyche, she raised as a daughter, then alienated and sent into otherworldly exile. The reunion therein comes only in dream vision. But it's interesting that the most intense relationship CSL ever imagined was between siblings.
...in July 1963 he very nearly died. He made some beginning of a recovery; buy by early October it became apparent to both of us that he was facing death.
In their way, these last weeks were not unhappy. Joy [Jack's wife, dead of cancer] had left us, and once again--as in the earliest days--we could turn for comfort only to each other. The wheel had come full circle: once again we were together in the little end room at home, shutting out from our talk the ever-present knowledge that the holidays were ending, that a new term fraught with unknown possibilities awaited us both...
Our talk tended to be cheerfully reminiscent during these last days: long-forgotten incidents in our shared past would be remembered, and the old Jack would return for a moment, whimsical and witty. We were recapturing the old schoolboy technique of extracting the last drop of juice from our holidays (24-25).