I found the whole of “Lamia” really interesting, largely because of the sort of betrayal in the story. Every version of Lamia’s story that I’ve read has involved some form of betrayal, and it’s almost always Lamia herself betraying her mortal lover. I kept expecting that in Keats’s version, but it never quite came; instead, we got four sort of peripheral betrayals, none of which were necessarily malicious in intent.
The last and most obvious was philosophy’s betrayal of the beauty of belief; Lamia here was a victim, as was Lycius, though he was also somewhat responsible, as he allowed Apollonius into the wedding. He more directly betrays Lamia by suddenly insisting that they marry, though it could be argued that that simply nullified Lamia’s own betrayal of keeping him in a love-ridden stupor, apparently unable to think for himself. The poem presents that stupor as a good thing, though, and the dissipation of the spell brings misery, so I’m not sure that Keats intended for two wrongs to make a right.
The betrayal that interested me the most, though, was the very first one, before we even meet Lycius. Hermes approaches Lamia, stuck in snake form, to ask her to point him to a nymph with whom he is infatuated; Lamia tells him that she helped the nymph magically hide herself in order to hide from the attentions of suitors exactly like Hermes, but promises to reveal her if he will allow her to regain human form in order to be with Lycius. I expected, early on, that Lamia was the nymph in question, that she had hidden herself in a serpent’s body as her form of camouflage, and that she was tricking Hermes with no intention of accepting his advances.
I was wrong: Lamia did, in fact, simply give up the nymph’s location and allow Hermes to find her in order to pursue her own love object. The situation is basically equivalent to Apollo bribing Peneus to turn the laurel tree back into Daphne. Though the nymph is initially terrified, as well she might be, the poem gives their ‘courtship’ only four lines before she is ‘won over.’ The issue is never addressed again; it is treated as pure exposition. The anthology’s headnote suggests that Keats may want readers to sympathize with Lamia, so I am left to wonder if he simply did not see that betrayal as a big deal.