My version of an explanation of relationships between spirit guide, soul holders, and their lovers
In my universe, usually spirit guides never take a separate physical form from the holder and is practically same soul essence, one in the same. The guide is usually only there in dreams and hallucinations to help those with distressing choices, survival, or simply a wakeup call to change something in their life for the better. Guides are also rarely 'permanent' or rather the animal may change out occasionally for specific purposes and only show up a handful of times.
Kaitlyn and other special magic users can potentially give guides physical forms and individual personalities. Even so, guides are still EXTENSIONS of the holder; therefore, the holder's feelings and personality traits still influence the guides to varying degrees.
For an example, Kaitlyn's initial crushes on Azriel, Cesaire, and Jacqueline gave her own guides varying degrees of that attraction. Now what each did with their attractions was up to them. Now onto Cosette and Vargr being a bit more special, Vargr is THE closest guide to Kaitlyn. Naturally the main guide would fall for a lover's main guide. (Vargr would've also fell in love with Aya's dove, hawk, black cat, or phoenix guides) In a way, Cosette/Vargr is a reflection of Past/Kaitlyn. How Kaitlyn and Vargr see both Past and Cosette is one in the same.
To also further add to influence of feelings, when it comes to Kaitlyn's lovers such as Past, Sky and her alters (@thesplitinvestigator), Lex/Fenrir/Victoria/Catalyst (@the-apex-hub), ect... all her guides will love them too in the same intensity as Kaitlyn (same thing for platonic friends). Even her guides like Corvo who *acts* very 'monogamous' would still see all of Kaitlyn's loves as their own.
As for the inverse (which would rarely ever happen) ...if Kaitlyn's guides stumbled upon a person they find trustworthy enough, Kaitlyn may feel a sense calmness/trust around that person later on despite not meeting them before (but her soul essence did). Again, rare scenario as Kaitlyn doesn't usually let her guides run around nor do they usually interact with strangers much unless needed.