How do I learn my triggers 😭

To make a long story short I was SAd and wasn’t with or didn’t talk to any man until my boyfriend. I had already gone through my own little healing process and had learned to live with that trauma before getting with him, but I knew sex was going to be a different story. There was only three times where I kinda freaked out and stopped everything but tonight we tried something new and it went soooo wrong. It’s really my fault because I forgot to consider what had happened to me and how what my bf and I were about to do could be very triggering but we did it anyway. When he pinned me against the wall I immediately got terrified, I didn’t see my bf anymore I saw my attacker and I dropped to my knees and started sobbing. He was really understanding and felt really really bad and helped me compose myself. The problem is is now he feels horrible like he did something wrong and I’m trying to tell him not to be upset and he’s saying he won’t be but I know him and he’s gonna think about it for a while:( I just feel so horrible cause I didn’t consider my SA and I had failed to communicate my triggers to him out of fear/embarrassment and just honestly not knowing what they are. I hate putting my sweet loving boyfriend through that and honestly myself. So how have any of you all figured out what your triggers were and how do I still try new things with my bf without the fear of having an episode like today. I just wanna move past that chapter in my life but it always hangs over me.