This is the root of his concern:

Soon these days of summer 
will turn to 
orange, yellow, brown; 
  lavish, yes-- garish even.

The glories of hot summer hours will not long abide;
 even the sun straining, tiring, 
   muscles aching, legs trembling
  longing for rest...
 and at that point 
 the twilight will have its say again.
 
Now... he sees her, envisions her, rather,
pressing her doubt against the chill window pane,
a patina of bonfire smoke settling,
covering sweater and hair alike

the thought is comforting, freeing almost; 
this too must end. Why fear this close,
when there have been so many before,
will be a number more?

And yet. And yet.