But our love it was stronger by far than the love Of those who were older than we-- Of many far wiser than we-- And neither the angels in heaven above, Nor the demons down under the sea, Can ever dissever my soul from the soul Of the beautiful Annabel Lee:
Even if death might seem to be the end of love, our speaker tells us that isn't the case for him and Annabel. Even though they were young, that didn't stop them from loving completely, and from knowing what they wanted.
He goes on to say that neither the angels in heaven or the demons who live under the water can stop their love. Nothing in heaven or hell can "dissever" (that means cut or separate) his soul and Annabel's soul.
The bottom line is that their love is eternal, and that nothing and no one can tear them apart.