I hate Halloween

It was Halloween and I spent it with my mom and my god mom's family. I was good friends with my god mom's 3 nephews, one was my age, and the other two were 2-3 years older. After we were done trick or treating, we all went back to their house and played for a bit. One of them, we'll call him R made it a game to scare me the whole night- creeping up on me, yelling in my face, just overall being weird to me. I was really tired and it was late, so R had convinced me to sleepover at their house and we all sleep in one room on pillows and blankets on the floor. I initially refused because I thought it was weird since my mom told me not to share sleeping areas with people of the opposite gender, but he once again scared me into doing it anyway. The door to the hallway stayed cracked just wide enough to see inside the room. It was probably about 3 hours into the night where he told me to take my jeans off so I could get more comfortable, since I'd been moving around since we laid down. I didnt want to, so he did it for me. He was stronger and I didn't want to make a scene so I let him, and after he pulled my shirt up as well. After R did the same to himself he then told the cousin the same age as me to take his off too and put himself on me, which he refused to do and fell asleep instead. R was touching me by then and he wouldn't let me fall asleep. Every time I did, he would pinch or squeeze me and scratch at my body. I remember he got mad at me because since I didnt have my first period, I was kind of missing the part he was looking for, but that didnt stop him. I remember waking up with my clothes still off and dried fluids on my thighs amd waist. I never told anyone, and forgot probably around a day later. Whenever I would talk to him after that happened, he would either spoil me with toys and snacks or be rude and shun me. I was so confused on why until I randomly remembered what happened. He treated me like I was different from everyone else, was always touchy and making fun of me when I started puberty. Now knowing what happened, I feel sick. I ended up becoming hypersexual after everything happened and I would often put myself in risky situations with older guys and anyone else who would give me the time of day. It disrupted my whole life and I didnt know it until now. Its been years since then and I feel like I should be over it, but im not. Im scared to get help because that means I'll have to tell my parents, I dont want them to be mad at me because I hadn't said anything sooner or for them to think im lying because it was so long ago. How do I get over it without any help? Its starting to mess with my daily life and im tired of the flashbacks and nightmares.