Sexual Abuse Support Group
Sexual abuse is a relative cultural term used to describe sexual relations and behavior between two or more parties which are considered criminally and/or morally offensive. Different types of sexual abuse involve: Non-consensual, forced physical sexual behavior such as rape, incest or sexual assault, or psychological forms of abuse, such as verbal sexual behavior or...

Even at no matter what age u or he is if u didnt want to be touched it shpuld not have happened at all.
Im sorry u were abused. Do u see a therapist at all? I suggest maybe u see one.
Hugs.
First of all, I'm sorry that this happened to you and I believe you. What happened was not just experimentation. It was abuse. You know it inside, trust yourself. If something feels wrong it was. If you still have doubts think about the difference between a 9 or 10 year old and a 16 or 17 year old. Think about the maturity level, physical size, knowledge difference. What do 9 year olds know, feel or think of sex vs 16 year olds? Is a 9 year old any match for a 16 year old physically or mentally? If you need to, think of kids you know now in those age groups. How would you feel now if you knew a 16 year old was doing the things you remember with a 9 year old? If they had a 9 year old give them a blow job? Then consider the power dynamic. I don't know about your family but in mine I was taught to listen to and do whatever my older siblings and cousins told me to. I was taught to trust them and look up to them. Your cousin betrayed the trust and love you naturally had for him, just as any kid would have for their older cousin. Instead he used that trust for his own pleasure. That is the definition of abuse.
This is something I had to work through myself. My brother molested me when I was 7 or 8 and he was 12 or 13. I had also repressed many of the memories and convinced myself that maybe it didn't really happen or maybe it was normal. I actually asked my sister, who he also abused, if it really happened. She confirmed what I knew deep down. As children it's impossible for us to understand what's happening or why someone we love would hurt us. We blame ourselves and we repress our memories because the pain of the betrayal is more than we can bear. It's the only way we know how to survive. It's actually quite amazing what we've survived as small children. I am proud of you for what you did to survive. It got you here today and look at you now! You were brave and strong enough to tell your mother and reach out for help! You were strong and courageous then and you still are!
As for what other people are saying or whispering, ignore them. I know it's easier said than done but remember people are stupid. They have their own issues, ones that you will probably never know about. Maybe they were victims but aren't strong enough to face it, maybe they are perpetrators and want to justify their own actions, maybe it happened to a family member or friend and they can't deal, maybe it threatens their worldview that people are generally good and the world is safe, maybe they are just stupid. We live in a culture that wants to excuse the abuser and blame the victim. Just look at the countless examples like Bill Cosby and others that have proof of wrongdoing, yet no matter how clear the truth is people refuse to see it. Things are slowly starting to change but it's still a long way off. People act this way because the truth scares them in one way or another. I don't know, they don't even know and it really doesn't matter why or what they think or say. What matters is what you think and feel. So, as hard as it is, ignore them. Stick with people who believe you and support you. Sounds like your mom is one, that is a major blessing. If you haven't already and are able, I strongly encourage you to find a therapist with experience in childhood sexual abuse. I love mine and she's been amazing in helping me navigate these confusing mixed emotions. She's helped me have clarity and helped me heal tremendously. Remember if someone makes you feel wrong or somehow tries to justify what your cousin did, you don't need them, they are not worth your time or concern. This goes for therapists, too.