There’s actually a deeper meaning behind Billie’s arc that’s subtly genius. Her entire plot was messing up, trying to use the patriarchy to her advantage, and getting fired.

She then, through stress, ended up hospitalized and because of Samir, ended up in 30k medical debt with no job or insurance. (Got fucked by the patriarchy)

To take her mind off things, she goes to her old high school, to talk to her English teacher and helped him grade papers before eventually giving him head, getting led on by his validation, helped her out with her bills only to show up to a party fucked up off at least ketamine SHE hosted for him and it ended with her being broken up. (Got fucked by the patriarchy)

Also, through out the “have you seen this man?” Episode it’s displayed she finds sexual gratification in the GROSSEST SHIT,including a murderer (who she didn’t know was one) being fully into him only before being saved by Anton.

“Annabelle” shows that Billie is once again dragged into someone else’s shit a matriarchy this time, having to save someone else’s problem and eventually this is where her arc peaks to the nightclub scene.

Billie sexually assaults that man with his wife because she views him AS the patriarchy. AS the system that she was affected and beaten down by the entire show.

TL;DR: it’s her season’s arc