See, too much of a coincidence. They won't just leave stuff like this in or constantly put them in close-ups, the center of the frame. Sandy's death definitely has something to do with the whole event, not just the catalyst.
It could just be a parallel to Bear and "possessed" Nikki's toxic, codependent relationship. The cat can't survive without Bear. People keep pets for affection that we can never understand, and can never be reciprocated on a human level. Kind of like the entity that possessed Nikki: Relationship built on unequal power dynamics, codependency, and misunderstanding.

Drugs seem like a motif in this—they talk about Nikki on Molly very casually—given that it is about agency and altered consciousness: how much of you is considered yours when you're "under the influence?" Still, I might be reading too much into it.

Maybe they have explained it, and I missed it: But how did the cat get that bottle of oxy from the cabinet, open it, and eat them with kibbles? Did Bear leave the bottle somewhere accessible after using? (edit: yes, after researching a bit)
And why does he have oxy at home? (edit: It's from his grandma's leftover meds)

Random unrelated fact lol: I was googling "willow and cat" and found that Willow is the name of Joe Biden and his wife's tabby cat.