Flashback During Sex - help

So I was raped about a year and a half ago. I dealt with it pretty well for the first few months and then began having more and more issues with anxiety/ptsd (I already had PTSD from a when my best friend was murdered a few years prior). Last night, my boyfriend of 4 months (he knows about what happened) and I were having sex. It started out great and at one point when we were in doggy I ended up more flat on my stomach with his weight on top. I just froze. A few moments later he noticed that I had stopped talking, moving etc. and asked if I was okay. I ran to the bathroom and cried. I was crying because of what had happened before and because I was so embarrassed that I had cried during sex. He came in to check on me and I apologized for freaking out. He hugged me and told me not to apologize but to let him know next time if I’m feeling uncomfortable. He said “you know I’ll stop if you tell me too. I don’t want to do anything to hurt you.” The problem was that I couldn’t tell him. I don’t know if he fully understands what I mean when I tell him that I froze. I literally couldn’t get the words out. I feel so lucky that he’s being so sweet about it, but I’m also terrified that he’s going to leave me because of this. Has anyone else ever felt like they’re afraid that their SO might leave them over something like this? Even if the SO hasn’t given any reason for you to think that? Am I just overthinking everything???