OOOOOOH this is such a good one, there are so many different places for Jacinthe to have gotten abandonment issues from.
Firstly, her parallel to traditional fairies, being something out of this world that doesn’t work by the same rules, doing all she can to be a part of it but still falling short on each and every step because she just doesn’t work in the same way everyone else does. She can’t change how she is or how she perceives the world and social conventions, and yet it drives people away even as she tries everything she could ever possibly do to keep them close. Nothing works to keep them from leaving her, which would lead her to develop a feeling that there is something deeply wrong with her, something inherently unlovable that drives people away.
(A neurodivergent metaphor? In my character analysis? It’s more likely than you think)
Also, through the mythological aspect, a lot of fae stories have topics of entrapment as a form of love. Humans being different enough that the way love is shown and perceived by both species is just so drastically incomprehensible that neither are able to even compute each other’s affection as such, and it leads to a feeling of being unrequired.
Now SECONDLY, because of her position as an “elite”, it’d make sense for people to want to use her a lot. For her money, her status, and then walk away once they got what they were looking for or no longer wanted anything from her. Having her not be a person but a mere symbol, a stand in for what they could get from her.
This could easily lead her to intentionally become more controlling, essentially an “If you’ll take advantage of me and leave, then I’ll use my influence and make it so that you literally can’t. Use me if you have to, but don’t walk away. Don’t leave me alone.”
