Hardy conveys Marty's sense of despair through descriptive imagery and other literary devices.
In the poem, Marty laments that the man she is infatuated with is oblivious to her state of mind and physical presence. He does not notice that she is chilled from standing still; to him, she is no more sentient than the 'woodland' which 'holds him alone.' This is because 'he has seen one fairer;' Marty knows that she is helpless against a competitor who holds a man so powerfully that he has become insensible to sexual cues from other women.
The sense of despair is amplified with the repetition of the phrase 'so many' in the sixth stanza. Marty's anguish is palpable, because no matter how hard she tries to prove to her co-worker that she is a worthy woman, he is impervious to her efforts. A sense of loss is conveyed in the words 'hope is gone,' further reinforcing the despair Marty fails. She will 'bear it ever/And make no sign' of her desperation; this imagery of a silent martyr highlights forbearance in the face of suffering and despair. The mood conveyed is that there will be no change to Marty's circumstances no matter what she does.
In Part II of the poem, Hardy extends the sense of despair through the use of personification. The repetition of the word 'sigh' indicates that the trees share the same miserable existence as Marty. Like Marty, the trees are helpless to change their personal circumstances. They are 'voiceless' even though they sigh. Since Fate has not decreed that they remain seeds, they must daily face the relentless power of nature 'in this bleak spot;' the trees must 'grieve' through 'storm and drought,' 'unable to leave' or 'change its clime.' Here, the sense of permanent impotence reinforces the despairing mood of the poem. The last lines of the poem hint that even the prospect of death will provide no solace.