Shutting down during intimacy

Hi everyone!

I'm here to talk about some issues I've experienced with physical intimacy. I have an extremely hard time communicating at all during or leading up to intimacy. I think I get so uncomfortable around it I struggle to speak. If things are going badly I even seem to shut down and can't even move away. I had an ex who was EXTREMELY rough in the bedroom and I would always tense up and was unable to say or do anything. sometimes I would cry but he never stopped or seemed to even notice that I was tensing/ flinching/ crying. I need a way I can communicate, that is nonverbal for intimacy. I was thinking maybe touching my partner in a certain way that is fairly simple, but not something I could do on accident. the hope being I'm able to move and don't completely lock up. I need a 'yes/more' signal and a 'no/stop' signal.

I'm actually just now figuring out I have autism which is making learning about myself and my needs a real journey. I'd love some some advice! If anyone knows any good ways to communicate even when very overwhelmed or tips of sorts. thank you so much for your support!