3 ideas
The title frames passion as an illness with an onset, a crisis and a breaking point. In this framing, disillusion is not the failure of love but the fever breaking: the return of a clear, cooler perception that desire had suspended. It treats infatuation as a temporary altered state and not a stable judgment about the other person.
Havana's winter is brief and mild, a slight deviation in a city defined by heat. Setting an affair in that season casts the passion itself as out of season, an intensity at odds with its surroundings. Reading the weather as a gauge of the inner state, and not as backdrop, lets the city's small anomalies mark the lovers' small dislocations.
The novel treats desire and intimacy as conditioned by the material and social texture of the city where they happen, not as purely private experiences. Read this way, a romantic disillusion also registers the setting that contains it, and the private arc becomes a way of seeing the city.