(1) Contrast (contrast, foil) technique. The first sentence is about drinking and talking happily in the spring breeze of peach blossoms, and the latter sentence is about being apart for ten years. We miss each other affectionately only when we stay up late and read at night every day. This writing fully expresses the deep nostalgia for friends and past years.
(2) The first two sentences express the helplessness of being separated by mountains and rivers and unable to meet each other. The chin couplet expresses the longing for friends in the comparison of the past and the present. The neck couplet fully expresses the praise and expectation for Huang Jidu, and the last couplet expresses There is not only sympathy for Huang Jidu, but also sadness for the official career of his friends and even the poet's own political fate.
(As long as the meaning is correct)