The narrator is one tough nut to crack. We rely on him for everything. He controls the flow of information and he's our only source when it comes to Ligeia. The problem is, he's totally biased – he loves Ligeia and hates Rowena, has a terrible memory (it's "feeble through much suffering," he tells us in the story's second line), and he's often high on opium. He's what teachers and literary scholars like to call an "unreliable" narrator; in other words, he's pretty hard to trust. We're just not sure if he's telling us the truth.
This leaves us with a problem: How should we react to the narrator's story? Well, we could praise our narrator for is his honesty, at least when it comes to his shortcomings: he tells us that he has a bad memory, that he's addicted to opium, and that he hates, hates, hates Lady Rowena. He's also careful to hedge any of his more unbelievable statements – maybe, he seems to say, I saw some red drops fall into Rowena's drink.
In the end, the narrator is little more than an observer. Some have claimed that he's really a delusional, opium-crazed murderer (You can read about that in an article that's innocently enough called "The Interpretation of 'Ligeia'" in the "Best of the Web" section), but that's a pretty outrageous explanation. The narrator may be angry, and if his taste in home decorating is any indication, a little nutty, but he's mostly lost. All he really wants is for his beloved Ligeia to return. It's a powerful and sort of childish desire, but it's one that seems to be fulfilled in the end.