Someone has written a letter to a person they once shared a close bond with, and they suspect it may be the final one. The speaker wants the reader to remember the time they spent together, including the stretches when they were apart. The wording is a little tangled there, which fits the speaker's mixed feelings about what the relationship really was.
Throughout, the speaker insists the letter holds something real: "my soul," "my heart." The image of the soul burning into the reader suggests an intense, almost painful need to be felt and remembered. Yet there is doubt too. The repeated "I wonder" shows the speaker waiting anxiously to learn whether the message ever landed.
The mood is quiet, sad, and resigned. The short, simple lines and repeated phrases feel like someone circling the same thought. The last line, "With this it all ends," closes the poem with a sense of finality, as though the letter is both a confession and a farewell.