The first stanza is about the two lovers parting in tears because one of them is obligated to leave the other to go to the sea.
In the second stanza the speaker of the poem, the lover, contemplates how the world is nothing until it's explored and put on a map, then it becomes all. The lovers' world is "all" to them as well because of their love. But now, that world, their heaven, is dissolved with tears of parting.
In the third and last stanza, the lover that is about to depart asks the lover who stays to not weep his death, to not sight too much for him, which means that the sorrow is too much for him to bear, but also because it might bring upon bad luck whilst on the sea-he's not dead yet, and he hopes to return.
