Molested by family member

When I was 7 or 8 I was running up the stairs when my grandpa grabbed me by the waist and dry humped me. Then when I was 11 my autistic cousin sat on me and held me down while he played with himself. I never said anything because I didn’t want to destroy our whole family and have since repressed and rationalized both incidents. Today my sister and I were in passing talking about how f-ed up our childhood was and I mentioned being molested. She didn’t believe me so I mentioned that it was done by members of our family and she still didn’t believe me. I have been to counseling but always lied about my childhood and my assault history. I don’t know what to do, now that she knows who it was she says that I have ruined her life and made her want to kill herself. I know she won’t actually harm herself but I need help but after today, I don’t think I can trust anyone enough to tell them.