When I was little my older sister did some really bad things

When I was little my older sister did some really bad things to me. I am not going to go into detail as given what this group is, I think it's implied. Anyways, she has some mental and physical challenges and has required a lot of care from our whole family for my entire life. For years I just pushed down the memories of what she did to me as I didn't know what to do with them. But as I've gotten older it gets too harder and harder to push them down. Do to an on going medical situation my sister is house and couch ridden and has been for close to two years. A few months ago my parents were looking into getting her mental help and talked to me to find out more of what she did to me when we were little as there was only so much they knew. I finally told them what happened, they believed me and said they were sorry but don't due to my sisters mental and physical condition (which means she handles any conflict or emotions that aren't hers by throwing a tantrum) and due to the fact that we were both young, they have decided that she was just a confused kid and no further action or discussion needs to happen. The problem is, now that I have actually put what happened into words, I can't push it down at all. I feel it in full and don't know what to do with this. I feel it every time I look at my sister and don't know how to handle that. I don't know how to just be kind and friendly to her because I don't know how to exist around her. Is there any advice that anyone can give me of something they did to begin to come to terms with this? Or to maybe feel a little better? I don't even really know what to ask for I just don't want to feel alone.

I'm very sorry that happened to you. Hopefully your parents will get more help to figure out what would be best for everyone.
Are you under 18 years and living at home? For one thought maybe you could find ways to take breaks away from the family such as staying with a friend or family on the weekends. Everyone is different and our circumstances. You need to do what you feel is best for you. It depends also if you have to live under the same roof as her and if that's the case like I said it would be best to get out of there as much as you can until you can move out. How old were both of you when the abuse happened?
You are definitely not alone there are so many families that have had the same thing happen. I think its good that you were able to tell your parents although I'm sure it was very difficult. I wish I had something more to help you.

Thank you for reaching out, it really means a lot. To start yes, I am under eighteen and will have to live at home for around two more years. I have a plan to move out as soon as I am able so I have that going for me. What happened with my sister happened repeatedly for about two years, from when I was four, to when I was six. My sister was around ages seven and eight. She was a kid too which is part of what makes it so hard. That fact makes it really difficult to be able to grasp what happened since she was so young and I don’t really know how to wrap my mind around that. I have pushed all of this down for so long so right now I am still just trying to come to terms with everything so I feel like I can have some control back. I have another sister who is an adult who I spend time with often, and I am able to spend weekends with her sometimes. I can also drive so I am not dependent on my parents for help to leave my home. Thank you again for reaching out, it feels strange to talk to someone about this stuff since I haven’t really done that before, but I need to get some of this stuff off my chest.