NTA. I feel for you. You need to be able to have your own life. Your parents need to look into professional help and caretakers. You are not a built in free caretaker. Think about changing how you put things about your sister though. She did not choose to be born. Maybe word it "my parents should not have had a child they are not willing to take care of" instead of she shouldn't have been born. Anger for how you were pushed and not able to have a normal life is understandable but you are old enough to be able to hate the way your parents behaved while still having love and compassion for your sister. Hating and saying cruel things about "a 3 year old" is asshole behavior, you know your sister is in no way at fault.