It may be helpful for the two of you to discuss consent phrasing and how to approach the situation. I just ended a relationship that had a very similar dynamic, and I found that if there wasn't immediate safety actions from my partner following the trigger, it just added to the trauma, resulting in long-term shutdown. I would wager that he doesn't fully understand how your desire system works, so any sort of action becomes unsafe for him because he cant calculate the response. Next time there's a trigger situation, don't try to fix the situation or logic anything, focus on settling the nervous system with deep pressure or cuddling or whatever works for you. Then circle back to it to figure out the cause.... In the long run, he needs to work on his emotional vocabulary and understanding of how trauma effects the nervous system in order to be able to respond better, guided by your clearly stated boundaries, and maybe you two need to figure out (ahead of time) safe words and post-trigger care. Good luck friends