My favorite hypothsis is that behind this closed door is Bella's dungeon.
Maybe her husband caught she and Jill in the act there and that is why he left. Hence why they don't talk about whatever happened between them when sharing Isabella's bed in this episode 5.
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NICE catch my friend.
Here's my new crazy theory (tinfoil hat on
): I think that the room might contain her stuff from the time of her youth. When she was happier, perhaps a bit rebellious? What I mean by that is she literally imprisoned there her happy self. Why would she want to cut herself from the past? I see two possible explanations (they might be actually connected) and both of them are based on guilt:
1. older Bella thinks that younger Bella is responsible for her parents' deaths. She told us in the new episode that they argued contantly while she was living with them. It changed for the better when she moved out but still. She's what? 35? And both of her parents are already dead? I would keep that in mind. And where did she move to? To her husband's place? If that's the case then why did she move back to har parents' house?
2. it was her husband that manipulated her into becoming submissive, devoted wife. But at some point she did something to spark his ire that caused their relationship to collapse. But by that time she was addicted to him. And thus her guilt was born.
I know, it might be a bit far-fetched
but let me know your thoughts anyway.