My sister [31/F] was sick and thought she was going to die, so she told me [27/F] family secrets; she lived and I don’t know what to do

Posting to a throwaway for reasons. My sister and I are very close, we tell each other everything. She was adopted as a baby since our mom struggled with fertility, and I was the “miracle baby.†Our parents love us both, but they totally give her older sibling privilege, even now they we’re both adults. They tell her everything, she knows about stuff weeks before I do, but I’ve never been very bothered by it. Also, our mom can be a bit distant. Ever since I was in high school, she’s struggled with holding a job, and always had a tendency to withdraw for a few days. I was told by our dad that it was because of her issues with depression. I’ve never taken it personally. Yeah, it can be difficult somedays, but she’s a good mom. She goes on frequent vacations and lives in another state, so we don’t see each other all that much.
Anyways, my sister was really sick and ended up in the hospital. About a week and a half ago, things got bad and she was put in intensive care. Both of us were really freaked out, and she thought she was going to die. Like, my sister was making calls and telling people she loved them. It was scary. When my sister was admitted to the ICU, she told me she didn’t want to die without telling me some things. So, she told me that I wasn’t my parents’ child. Our dad had an affair with our mom’s sister, and when our aunt got pregnant, our dad convinced our mom to stay with him by promising she could raise the baby- me. She said yes, obviously. And as though telling me all that wasn’t enough, my sister told me that our mom has been addicted to drugs and alcohol for roughly the past decade. I didn’t know what to say, and she just kept going, saying our mom goes on “vacations†that are really trips to rehab. I just felt frozen, like I couldn’t say or ask anything. I didn’t.
My sister is okay now. Our parents are with her. I don’t have any idea what to do. I can’t look at my mom without thinking of all the lies I’ve been told. I can’t look at my dad without feeling betrayed. A few days ago, I asked my sister about it and asked how she knew and she said they’d just told her. She asked me not to bring it up with our parents, since they’d be angry with her for telling, but how can I not? What do I do? Who can I trust?
TL;DR: My sister was afraid of dying and told me that I was adopted and our mom is an addict. I’m lost.


Source.

These people should write for soap operas