How do you tell parents, your getting touched in a "inappropriate" way ? ( long )?

The coach of my gymnastics team has been acting in a very inappropriate way. During our first team training session, he has extremely nice and he told us that we could come talk to him about anything. A few months later he started to get really touchy. At first we just ignored it because sometimes coaches have to touch the gymnasts, but than he started massaging us, patting us on our bums, kissing us on the lips, forehead, and cheek, making us sit on his lap, etc.. My mate Emma and myself told him that we weren't comfortable with him kissing us and asked if he would mind not doing it. He told us that " that was just his way of showing us that he's proud of us and we'll get use to it." When he said that Em and I thought we were just overreacting. None of the others girls on the team were complaining. Than 3 months after that our team captain and also a very good mate of mine, Courtney had stopped coming to trainings. She never misses them. So I went to her flatt and I asked her were has she been and is everything okay ? She told me "no". Court told me that she doesn't want to be around our coach anymore. She went on to tell me that one weekend he had invited her to have lunch in London with him. She said since she was captain, in a way she felt obligated to go. She than said that after lunch they had went back to his flatt because he wanted to show her old videos of his other former gymnasts, she said the only reason she agreed was because he told her that his girlfriend would be there. When they had gotten there, his girlfriend had gone out to visit family. She said while they were watching the videos, he had started putting his hand up her skirt and started kissing her. She told him to stop and she had started to cry. He told her that " he could see that she wants it" and "how he wouldn't hurt her". she told me that it hurt so much and she trusted him. She said she didn't want her first time to by like that. She said after, he helped her put on her clothes and gave her a kiss on the forehead and asked her to keep it their "little secret" She said she keeps having nightmares and she wants to tell someone but she thinks it's her fault for "giving it to him".The next day me and the rest of the girls met at a cafe and discussed the problem. They said they've all been touched by him ( on the bum, chest, private areas, and Brooke was also talked into having sex with him ). I really want to tell my mum and dad, because they know something is wrong. I can't focus on my gymnastics or school work because I'm always nervous about being around my coach. I've been touched by him before and I keep thinking what if he does the same thing to me that he did to Courtney and Brooke? At the same time, me and the other girls feel guilty for everything and that we must have lead him or something in those months to make him do these things to us. Our coach is very young and very good hot.He just turned 23 last month and we've always been able to trust and connect with him. Most of us on the team or 16,17, and 18 years old. He was also a very good coach. I want to tell parents what has been going, but I'm scared. How should I tell my mum and dad ? I was going to write them a note, but I got nervous. I think talking to them would be better, but I'm not sure what to say and how say it ? What if my parents think it's my fault for letting it go on for so long ? Another thing that were worried about is that he's having a selection trial for new girls that might be joining our team. We one of the girls and we told her that he can be quite touchy and inappropriate at times and she didn't believe us. Laura told us that he seems like a very sweet guy, and he's really cute and he told her that she such a "beautiful" gymnast and he thinks that she could go very far. I feel very confused. None of us want the new girls to have to go through what were going through went him, but at the same time, I told her how touchy he can be and she didn't believe me. I want to tell an adult, but what if they don't believe us, just like Laura didn't.