Confused

So when I was in 4th grade my brother who’s a year ahead of me started learning about sex and how it all works and I was a naive little girl. He came home one day and mom was at work and dad was deployed and he told me he how sex worked and that since I was to little nothing would fit in me and said he wanted to try to fit his dick in me. He took me to the office and tried and mom came home so we stopped. I didn’t know it was wrong and over the next few weeks he tried to get me to give him handjobs and blow jobs and honestly I didn’t know it was wrong I mean that’s my brother why shouldn’t I trust him he would never hurt me. He stopped after a couple weeks and never mentioned it again. I honestly thought I dreamed it for 11 years. Recently I told my boyfriend bits and pieces about what happened but he wants me to confront my brother and tell my parents about what happened even though I’m not even sure it happened. I’m just so confused st this point I want to have some sort of confirmation I guess so I get passed it but I have no clue how to even confront my brother let alone even tell my parents. This is the first I’ve ever even spoken the whole thing and the more I think about it the more real it feels and the more crushed I feel and I’m honestly so lost. How could an almost 12 year old do that to his 9 year old sister