The same thing happened to my father when he was younger, his two-year older sister had abused him, but she didn't know it was wrong either. He learned to forgive her because there was no malicious intent or feeling that she was doing something wrong. Do not fret, dear. You are a strong person, and you are not a sexual abuser. I am sorry to hear you have had things happen to you that caused you to believe it was okay. I'm sure your sister loves you very much. I believe it would be best to sit and talk about it with her. It might be hard, but I promise that the closure will provide you so much relief.