A Different Light — Elizabeth A. Lynn

Jimson had twenty years to live. Or one.

Twenty years if he stayed in space-normal, where his disease could be treated. One year if he followed the Starcaptain into the Hype -- the "not-space" that trip was the only way to the stars, where jeweled voyagers sailed the light-centuries in color-shifting ships; humankind's outriders, star-burned lovers to a Universe heavy with suns...

This is the story of that year.