Here a speaker pours everything into loving someone else. The opening lines are physical and intense: blood, a "volcanic" body, breath offered freely. The speaker holds nothing back, and the person addressed also lives inside the speaker's mind as a kind of secret image.
Then the mood shifts. Time begins to feel heavy, with every moment casting a shadow until the speaker "can see nothing which remains." Trying to "fit you into my thoughts" suggests the beloved doesn't sit easily there, and the effort feels strained. The closing image makes this clearest: a man on the shore waiting to see the last wave. It's a patient, almost hopeless picture, since the sea has no last wave. The poem suggests a love that is passionate but unanswered, or at least uncertain, and the speaker is left watching and waiting. The overall feeling is devotion mixed with longing and quiet resignation.