I think you are normal. The first person I shared my abuse with was a woman in AA I knew and trusted. She pointed out that I had expressed no anger toward my abuser. It is all confused in our heads about that. She said he was a sick bastard. I had honestly never thought that. I have not told my wife yet. She is a southern girl, and has a temper, especially about family. She could potentially do great harm the person. No kidding.
The ages of him and his sister are close. Not sure of the friendship dynamic there. I probably adds to the guilt and confusion if he got an erection during the course of all of it. Our bodies respond, like it or not. We can be confused and betrayed. He probably feels partially to blame? I had to get it in my head that it was not my fault, I could not consent at 8 yrs old.
Keep on talking. Trust is built over time. It sounds like you are on the way.
I feel more like I do now than I did when I got here.