Relationship/Trauma troubles

Ive been with my girlfriend almost 4 years, and ive recently been considering proposing. shes made me unbelievably happy and I want to stay with her as long as I live.

However, last month she asked for a specific sexual act that ive repeatedly said that I dont enjoy, and I told her that for her birthday, ill do it as long as she wants(I know, birthday acts arent as meaningful, just keep reading).

Heres the trauma part though...when I was in high school, my closest friend of 5 years, came to me and said that if I dont stay away from her, she'll tell the police "what I did to her". Long story short, she was severely mentally ill and had convinced herself that I had snuck into her house in the middle of the night, and assaulted her in the specific act that my now-girlfriend wants. Ever since that, ive been terrified of these allegations being used against me daily because men have been charged on less evidence. I've also been terrified of that specific act. Adult content, the mention of it, doesnt matter, it terrifies me at any point its brought up.

back to today though, we went to a hotel for her birthday after taking her out. we had a good time and did other acts, then, when she asks for it, I have to break the promise of doing that act because of my fear of it. I'd been trying for the last 2 or 3 months to be more comfortable, but to no success.

last night, when I was asleep, I woke up to her telling me that I broke her trust and she is going to be withholding intimacy because of what I did.

in any other situation, id be completely understanding and not argue, however, she has sexual trauma too and has had to go back on things shes said, or stop mid-intimacy, or even stop intimacy because of her fear for 6 months at one point, going as far as not letting me hug/kiss her because of that fear... and ive never once given her any kind of punishments for that. it feels like im being punished for being afraid and it doesnt feel fair to me.

Someone please give me advice or a severe reality check about this.