There is a horrible situation going on in my family and I need some advice.

It’s a long story but I’ll try to make it short and coherent.
I am 19, and since I was young, I’ve had a weird childhood memory of one of my cousins, let’s call him Ben, (who is 11 years older than me) threatening me and touching me in a sexual way

. I won’t get into details but I remember crying and him only stopping when his sisters came in the room and saw what was going on. Now I was really young when that happened, but for some reason I still remember very clearly everything that happened.
All of my life I never talked about it to anyone, because I was wondering if it had really happened or if I had imagined it. As a child, I wouldn’t even think about it twice except a few nightmares, but when I became a teenager I started to understand what had happened to me. I never told anyone about it though.
However, recently I had been thinking more and more about it and having more nightmares, because this cousin is getting married this summer so his name would come back often in conversations at home. One day I got so upset that my mother asked me what was wrong, and I told her: " I remember what Ben did to me". Her face looked like this:

She asked me what I remembered, and I told her everything. She told me that I was 4 when it happened (so Ben was 15), that her and my father were travelling so I stayed at my aunt’s house, and that when they came back I told them that Ben had “touched my parts” and that when they confronted him about it he denied it, but my aunt and my uncle apologized for him. I was really angry to learn that all that time my parents knew about this and they never tried to talk to me about it, that I had to deal with this alone.
On the next day I was thinking about this and I was crying, so my sister (2 years younger) asked me what was wrong. I had never told her because I didn’t want her to hate our cousin because of an old memory that I didn’t fully understand. Now that I knew that it was real, I told her what happened. There was a silence and then she told me that he had done the same thing to her* at our house* when she was 6 years old :bigyikes: Only she had never told anyone about it because Ben made her promise not to and since she was a child and he was 19 she was scared

I was completely devastated to learn that my sister had been dealing with the same thing all this time.
On that night we told our parents to come in the living room and my sister told them that it happened to her too. They just said: oh…really. I told them that I refused to go to Ben’s wedding, and they agreed. My sister isn’t going either.
Now I can’t stop thinking about this whole story, I really hate Ben. I know we are supposed to forgive, but this is so hard :crying: I had almost come to terms with what had happened to me, I was always friendly with Ben even though I disliked him. But now I know that
- he lied when I told my parents what happened, and said that I invented it (as if a 4 year old would invent something like this)
- 4 years later, as an adult, he did the same thing to my little sister

I am also really angry at my parents, for never telling me what happened, even though they had
no idea whether I knew or not. Also, I can’t believe the fact that someone would do this to their daughter and not even admit it and they would keep inviting him at our house, to our birthday parties and all.
This summer he is getting married so we have family members coming from different countries, and it will be awkward when my sister and I won’t show up to the wedding. I also feel horrible for his fiancée, a wonderful girl that I get along with really well since they started dating 8 years ago. She probably has no idea about the things he did to his cousins. I don’t think I would have the courage to say something though, especially when they are getting married in less than a month.
I feel, angry, sad, humiliated and confused. I just don’t know what to do.