3 ideas
The novel's governing premise is that love operates under a quota: of every five people who love, only one will be happy. Framed this way, heartbreak is the expected outcome rather than a personal failure. Each individual story becomes a question of who gets the one happy slot, and at what cost to the others.
The novel argues that love is a reciprocal act that no author, planner, or pursuer can manufacture. Trying to secure it through craft reproduces the very powerlessness the writer is trying to escape.
Read Lucas's stories as offerings addressed to one reader, not as neutral art. Each ending he revises exposes what he fears about his own chances. Seen this way, the failed endings of the other lovers stand in for the outcome he dreads in his own pursuit of B.