The speaker of this poem, who is mourning the death of her lover fifteen years ago and talking about how she has reacted to her death, wants nothing more than to avoid spending too much time reminiscing and remembering her lover in case she is plunged into a depression and sadness again that she might never be able to return from. Note how this is introduced in the final stanza of the poem:
And, even yet, I dare not let it languish,
Dare not indulge in memory's rapturous pain;
Once drinking deep of that divinest anguish,
How could I seek the empty world again?
This final stanza follows a description of the speaker's initial sadness and grief, and then, slowly and painfully, even though she has never had another lover, she has managed to cope with her pain and live her life once more. What she fears above all else is that if she were to "drink deep of that divinest anguish" once more, she would never be able to live in the "empty world again." Note the use of alliteration through the repetition of the "d" sound, which seems to interestingly express both a fear and also an attraction, as the speaker tries to force herself not to think of her lover, which she clearly wants to do, as this anguish is described as "divine" and she wants to "drink deep" from it. The speaker therefore wants to avoid dwelling on the past, out of fear that she will not be able to live at all in the present, so barren has it become without the presence of her lover.