Need advice *trigger ⚠️

Looking for advice, I was told to post here idk what to do. My fiancé told me a secret that he’d been holding onto his entire life. He told me that he was sexually abused from the age of 6-13 by a family member and no one knows. He broke down and told me how it effected him mentally and that he struggles with this. Although I appreciate him telling me and I’m supporting him the best way I know how, I cant be around this family member and it’s frustrating. She showed up over to another family members house a couple of days ago unexpectedly and I couldn’t talk or speak to her and my anger towards her is constantly progressing. I want to respect his wishes and not tell anyone, but I can’t come to family functions or around his family and she’s around. Others in his family noticed that I didn’t speak and my anger towards her but don’t know why. how do I explain my issue with her without telling my fiancé’s “secret” that he’s ashamed about and thinks that no one will believe him? I don’t want everyone to think I have an issue with them when I’m no longer attending events, and I can’t tell them why.