In Emily Bronte's "The Night is Darkening Round Me," each stanza (four-line grouping of lines) reflects the sense repeated at the end of each stanza that the speaker cannot go.
The words, as well as the repetition of "cannot go" give the sense of being trapped.
In the first stanza, the darkness encircles the speaker, and without light, one could feel unable to move.
In the second stanza, the boughs of the trees bend down, weighted more closely to the earth than usual by snow, also providing a sense of imprisonment.
In the third and final stanza, the speaker knows no release:
Clouds beyond clouds above me,
Wastes beyond wastes below;
But nothing drear can move me:
The closing line of the stanza (and the poem) portrays a sense of "enclosure." Clouds are above, wastes below and beyond, but nothing can move the speaker.
The question I find, however, is whether or not the speaker wants to go. The first two stanzas end with "I cannot go..." in some form, but the final stanza changes with an important shift: "I will not, cannot go."
Up until this point, we have perhaps felt the woman was trapped against her will. The one phrase "I will not..." provides us with the sense that she chooses not to go: she refers to her "will."
To truly understand the possibilities of this poem, we now need to look at the structure of the poem and the content. The structure indicates by providing images of "enclosure" that the speaker is trapped. However, perhaps she is with a lover, or visiting friends she does not want to leave, and as the weather conspires against her, it is possible that her "imprisonment" is welcomed.
The line "But a tyrant spell has bound me..." might at first sound like a spell of someone or thing that uses force to hold the speaker.
However, if a lover were casting a tyrant's spell, it could simply mean that the speaker found no strength or desire to say good-bye or take his/her leave.
In the last line, "But nothing drear can move me," may also provide a sense that this "captivity" is desired. "Drear" is a form of the word "dreary," and means: gloomy, boring or sad. The speaker is saying that nothing "negative" can move her.
So with the images of being enclosed by nature: darkness, clouds and trees, with the sense that nothing sad or gloomy can convince her to leave, we can assume she is "trapped" where she wants to be.
Recall that the structure is what provides the images of being closed in, but specific lines within the stanza portray a welcomed delay. First she cannot leave, perhaps because of the weather. And after the fact, she decides she "will not" go.
Hope this is of some help. This is a great poem.
(Thank you, too, for providing the poem's text.)