Speaker
The speaker is not identified in any tangibly recognizable way. The reader is not privy to the age or gender of the speaker. This lack of concrete description succeeds in giving the character's situation a universality.
What is known for sure is that the speaker has lost someone who was once very close. The setting of the poem is a park-like place featuring a garden and fountain. The speaker explicitly identifies the area as the site of the last meeting with the person they have lost.
It can be inferred that the absence of this other person from the speaker's life is not by choice of the speaker. The setting is a place of good memories that have become sad memories as a result of losing the other person.
The Lost Loved One
Even less is known about the person the speaker has lost than is known about the speaker. Not only is there no indication of age or gender or any other clues to identity but even the precise relationship to the speaker is a mystery.
In addition, the exact circumstance of this person's absence is left unexplained. The context of the speaker's memories equally fit the possibility that this loved one has died as it does that this person initiated the breaking up of a romantic relationship. Either possibility could be applied, but neither is definitively implied. As a result, this is a poem about one mysterious person recalling the memories of another mysterious person.