We are all here for a place of safety and support. I am one of those older people you talked about. There is no such thing as your failure to say no.
Where would you have gotten the power to make no stick. How would you know if there were other sources of feeling good, or at least not as terrified.
At 20 you are ahead of the game. My sexual abuse began when I was 11 and continued till I was 16. Several different perps. But I sought no help until I was 37,and I still thought I could minimize what happened. It overwhelmed. I have been diagnosed, medicated and therapied for 20 years.
We all have different stories, but we all are just the same. Welcome, new ground is right, don't push yourself, take it easy. I hope you find what you need.