Elysium by Jennifer Marie Brissett

Adrianne/Adrian moves back and forth through recent time, switching sexes and situations—always with the same people, albeit in different roles—with each life interrupted and restarted by a mysterious computer code that he/she is occasionally vaguely aware of. The one love in her/his life is Antoine/Antoinette, who appears in a variety of roles such as lover, sibling, and friend. But sooner or later, Antoine/Antoinette is always lost. As the fragments of story grow larger and more complex, Adrianne/Adrian continues changing, but Earth remains the same dark place, haunted by an event that alters or kills most of the population.