"Annabel Lee" is about a beautiful, painful memory. The speaker of the poem is remembering his long-lost love, Annabel Lee. The speaker knew Annabel Lee many years ago, when she was a girl, and they both lived "in a kingdom by the sea." Even though they were only children, these two were really, seriously in love. So in love that even the angels in heaven noticed and were jealous. Maybe that was a bad thing, because our speaker blames the angels for killing his girlfriend. Apparently a wind came down from the clouds, which made Annabel Lee sick and then eventually killed her. When this happened, her relatives came and took her away from the speaker, and shut her up in a tomb.
Our speaker wants us to know that his love for Annabel Lee wasn't just a teenage crush. A little thing like death isn't going to separate him from Annabel Lee. Not even angels or devils could do that. He still sees her everywhere, in his dreams and in the stars. In fact he still loves her so much (here's where it gets really weird) that he goes and lies down with her in her tomb every night. Creepy.