I love the creative use of the endings mechanic. Each 'pass' has such unique effects as well, the wavy 3-colored one is my favorite!
Spoilers:
My fae senses were tingling by the 3-4 pass, It's so fun to deduce too! If the author said yes their body instantly recovers, if they stay they slowly die. Especially its emphasized how amazing the author is, and won't stop writing after meeting him. This interpretation of leannan-sidhe is quite amazing. He seems more desperate to break up than you. Both the author and the fae are selfish and stubborn, that's what made their relationship so believable in the short glimpse we see of them. I love that he says he is a bad actor, which is true because he can't pretend not to love you. All three ending features the bittersweet fate of a vampiric muse.
My favorite is the one where the conversation at the bookstore take place, "I love the author much more than you" is both heavy and comedic. I feel that the 3rd ending feels fitting, The fae love the author both for their person and their art combined, the author also both love their art and the fae. Therefore that's the only ending they could achieve that fulfills both of their needs.