The problem character and scenes:
The character with most unclear motivation is Psyche. This version of Psyche diverges from the mythological one when during the era of the Romanticism movement she and companions somewhat manipulate Eros into challenging a vampire archer to a contest. Short version: Eros technically wins at archery but by shooting blindfolded Psyche with a special arrow he enables her to choose to remove the blindfold and look on the vampire. Psyche then acts as travel companion and lover to this vampire for the next couple centuries, much of it spent traveling across the US by rail or car and sometimes menacing or murdering humans.
Story-present: it’s the 1990s and most of the characters are in NYC. Eros, still miffed that he was manipulated and that Psyche declared herself divorced from him to be with a vampire uses his powers and arrows to stealthily shoot the vampire, causing him to them fall in love with a fashion design student at Parsons. It’s doubtful he really believes he can get Psyche back. But he probably want’s to break-up her relationship with the vampire. The fashion student isn’t anyone remarkable to Eros, but he is someone that Eros may be able to defend is the vampire’s type to explain this action isn’t too far beyond his duty.
The vampire (named Athen) then poses as a fine art student and successfully romances the fashion major (Julien) and the two have been dating.
Athen the vampire was probably still seeing Psyche during some part of this time he was with Julien, but it’s likely he’s been seeing her less and that their relationship was no longer as intimate.
At some point, Psyche gets motivated to do something?
Here’s where it doesn’t really make sense when I think about it objectively.
Apparently, Psyche locates Julien when he’s out on Black Friday (after Thanksgiving). She somehow gets him in a car with her. (Her child, Splendor is driving). Psyche reveals something to Julien. Could be that Athen is a vampire. Could be that Athen is still with her. She then presents Julien with a flashlight/torch and a knife. (Because her sisters gave her a lamp/candle and a knife?) For some reason, Julien decides to use the knife on himself. (Splendor I know is distraught to witness this and teleports away to tell someone what happened.) Others, including Athen, appear on the scene (they were already looking for Julien and the car was near their home by this time). Athen, not willing to allow Julien to die forces him to swallow his blood. It’s not clear exactly how conscious Julien was when this happened. We do know from later scenes that Julien is mad that he became a vampire against his will, though he does later regret trying to take his life on that occasion and is eventually at peace with surviving as a vampire.
Psyche’s ‘superpower’ is that she knows the mental state others are in. She doesn’t affect mental state or thoughts, she just knows them. So whatever her original motivation, it’s not clear why she wouldn’t have known what Julien would do or if she knew/understood his motivation she would go on. There’s no sign Psyche had personal animosity towards Julien.
It is possible she wanted Julien to see Athen for what he was the way her sisters in the myth wanted her to see Eros as the beast and have the option to kill ‘the beast’. Maybe she suspected that if Julien knew, he’d break up with Athen and then Psyche could just be with him again?
And if that was her motivation, it’s more likely her revelation to Julien was focused on Athen keeping his vampirism secret.
Also, it’s not clear whether Psyche knows that Eros is responsible. If she does know, it’s unclear why she doesn’t just reveal that to Athen. Maybe there’s a rule against this among her people? Maybe that seems more hurtful? Or, if she doesn’t know, does that help explain what she would be more likely to risk Athen being injured?
Psyche isn’t her stepmother. But here, she seems like she’s acting like her sisters or stepmother. Why? Is this irrational action her wake-up call that she’s become those manipulative people who hurt her in the past and she needs to correct and stop being OK with menacing humans?
Right now, there’s not enough information in the story to explain these motivations.
And neither Psyche nor Julien is a POV character (which contributed to me writing myself into this corner) so the reader always receives the news of these events after the fact (Splendor was a witness to some of it) or through a character arriving on the scene after most of it has happened. This enabled me to have weak writing where the POV characters just observe that something has happened without showing how and why it did happen.