Answer to the First Question: In the poem, the speaker is an observer of the Sun cycle in a city landscape, and the sun represents what the speaker yearns for. Along their journey to reach the Sun towards the west - which is the cardinal direction the Sun leans to hide itself -, the speaker describes the passing scenes of the landscape, and at one point, the feel of autumn air is remarked.
It is led to believe that daytime represents the spring and summer stations, being the lifetime of the speaker's efforts to reach their desires; the moment before sunset represents autumn, and in it the story reaches a climax in which the speaker's desires are at hand; night represents winter, and it depicts the worthlessness of the speaker's efforts to accomplish their dreams - even when they seemed closer than ever.
Answer to the Second Question: In the end, the stage of autumn defines the speaker's false hope - as they failed to reach their desires -, and the winter stage brings that realization afterwards.