When we talk about poetic form, this generally refers to the different sets of poetic "rules" a poem follows. In order to discuss poetic form, you must look at things like rhythm or meter, repetition/rhyme, and alliteration. Some poems follow no distinct form and are considered "free verse." Some poems, like sonnets, are carefully patterned to follow a planned rhyme scheme, a certain number of syllables per line, and a specific meter. Other poems may employ some but not all of the devises listed previously.
"Black Monday--Lovesong" is not free verse. First, it is written in rhyming couplets, meaning the end of every two lines rhymes. Each line attempts to maintain exactly 8 syllables. In this way, the subject of the poem ("love's dances") is personified in the rhythm of the lines. It is as if two partners are dancing in each line. The repetition of the first word "one" and later "and" keeps the poem flowing, almost mechanically, much like the steps of a dance. Ironically, it also heightens a tone of monotony, which clearly the poem is suggesting that love is monotonous.