Advice w sex

So I’m 19, I’ve only been w one person. I’ve been dating this new guy and we hit it off great- but when it comes to getting sexual I start getting anxiety / flashbacks. I’ve never been raped but ive been sexually assaulted and been in unpleasant situations. How do I work past it? This guy is willing to wait however long and even would be ok if we didn’t do anything. I used to be a really sexual person, but I don’t know what is wrong with me???