Why does the speaker of the poem lie down by the side of the tomb by the sounding sea?

This line comes from the famous Edgar Allan Poe poem "Annabel Lee," which was inspired by the poet's young wife.
The speaker describes the unrivaled love he shared with the titular woman, a love that was so pure and intense that the speaker accuses angels of being jealous of the young couple. This jealousy, he says, is why a "wind blew out of a cloud" and caused Annabel Lee to grow ill and die.
In the third stanza, the speaker indicates Annabel Lee's death with the use of "sepulcher." A sepulcher refers to an entombment. The speaker repeats this term in the penultimate line of the poem, which emphasizes its importance.
The speaker lies in the sepulcher by the sea because that is where his beloved is buried. The speaker describes how he stays there all through the night because he cannot bear to be separated from his love. Therefore, one could infer that the reason the speaker does this is because of his grief. He is not coping well with her loss, and he finds comfort in being close to her. Using the word "bride" in this final stanza where the speaker describes his mournful slumber also suggests that he has turned her tomb into a perverse form of marital bed.
Maybe the speaker believes he is forever wed to Annabel Lee and must show his devotion by never leaving her side—even if that means sleeping at her tomb.