Marguerite

Matthew Arnold's poem "Isolation. To Marguerite" is, as the title suggests, dedicated to Marguerite, who is presumably the lover of the speaker. This being said, Marguerite is never named specifically in the poem. According to the poem, Marguerite—to whom he now bids—did not have the same experience in love as the speaker.. Marguerite appears to have fallen out of love with the poem’s narrator, leaving his forlorn heart alone and without the joy of having its passion reciprocated. The physical distance between the two of them seems to have contributed to this divide. 

The Unnamed Narrator

The main character in the poem might then be identified as the unnamed narrator, who has been separated from his beloved, Marguerite; and yet, in all the time he has been "apart" from her, his love has grown more intense and his heart has remained "constant." In being separated from his beloved, his "faith" eventually reached the point of being unreturned. The narrator laments this loss and wishes he had thought about it sooner. He seems to believe that there is an inherent loneliness and solitude associated with living life as a human. Sadly, the speaker even goes so far as to say that this loneliness is merely a return “Back to…solitude again!”

In many ways, then, Arnold's poem here utilizes a fairly typical trope of romance poetry in forming its protagonist: the forlorn lover addresses his words of yearning to a beloved who has scorned him. However, he does not seem to truly blame his beloved Marguerite for having drifted away from him. While he has indeed hoped to become one with her, he now bids her "farewell" without any apparent bad feeling; he is disappointed with his lot, but the poem seems to suggest that isolation is always a possibility in human relationships.

Luna

The speaker alludes to several other characters in the poem who are not directly encountered, taken from myth. The first of these, Luna, is the goddess of the moon. She is a figure from Roman mythology. Arnold’s speaker refers to her as "chaste" and describes how she hung over her lover, Endymion, from far above in the heavens. Luna, however, knew she was meant to be alone. Since she is identified with the moon, there is no possibility for her to be truly integrated with the human world over which she watches. The speaker, however, did not feel the same isolation as Luna when he was dedicating himself to his absent beloved. At one point, he had evidently yearned for a closeness that he felt might one day be available to him. Unfortunately, now he is condemned to a loneliness he did not expect; unlike Luna, his heart must sustain itself now that it cannot be twinned with Marguerite's as it had once hoped to be.

Endymion

Though there are many versions of this particular myth, the story of Endymion reflected in the poem connects him directly to Luna. Endymion was a shepherd whom the goddess Luna developed feelings for. In order to preserve his good looks, Zeus sent the man into a deep sleep in which Luna could visit for a sexual relationship. According to this story, he fathered some fifty children of Luna’s this way. Though this tale is not particularly pleasant, the poet has spun the myth in a romantic light.