The verb “to dissever” means to divide or separate two or more things. The narrator believes that the love he shared with Annabel Lee was so strong that not even angels nor demons can keep them apart, even after her death.
"Coveted her and me...."See in text(Text of the Poem)
To “covet” means to desire something or to wish to possess something or someone. Poe’s choice of the word “covet” possibly alludes to the tenth of the Ten Commandments laid out by the Judeo-Christian God, who declares that “Thou shalt not covet thy neighbor’s wife” or anything belonging to one’s neighbor.
“Seraphs” are angels, which comprise the highest order of the Christian celestial hierarchy. Angels are traditionally associated with kindness, order, and purity.