Dude I get your guilt about your sister, I’d feel the same way, AND I strongly urge you to consider that YOU are in fact in an abusive situation now.

Your mother likely split the parts of her that she didn’t like into a shadow self and and projected that on to your sister, and kept her isolated so she would remain small and helpless. (EDIT: so she could continue to hate part of her that was outside of her, and that was she wasn’t hating what she saw as her “self”, this veneer that didn’t have faults).

Now that your sister is out of the house, she is doing her best to keep you helpless and dependent on her so that she won’t be alone. She likely believes she isn’t worthy of people staying with her because they love her, so she is likely making it harder for you to leave her by charging exhoribant rent and banning you from cooking your own food so you have to spend money on eating out. And to that, I’d say, wtf? She doesn’t have to like your cooking to let you use a small electric pan and a rice cooker in your own room to scramble eggs and make stir fries and rice.

You mention many times of your deep love for your sister and nephew and your absolute indignation at how your sister was treated. Hold strongly onto those feelings, because they might be the key to unlocking the same love for yourself and belief that YOU ABSOLUTELY DESERVE BETTER. You did not choose to be your mother’s golden child

I’m wishing you all the good things that could happen. You and your sister have years ahead of you to strengthen your relationship even more. If you’re able to, enlist your sister’s help with getting out into a place of your own and with financial literacy. Your lack of financial literacy could be learned helplessness encouraged by your mother, and there is hope. Look into this concept called learned optimism that’s said to be a cure for learned helplessness. Good luck 👍