Edited: I am not certain how else I can help. There is this lady that I am currently seeing:
There is one incident that happened a couple weeks ago during a meetup. I saw something happen that I wish I did not see, and I had no choice but to let it go. We did discuss this incident and I ended the discussion and changed the subject. I had also forgotten about this incident as well when she brought it up the next day in a text message and even expressed to her that I had forgotten about it and she changed the subject. Moral of this story.... Don't bring it up yourself if there is a possibility that he may have forgotten about it, especially if you know he will get all wound up about it as well.
I have also seen similar things happen with my father and mother as well since I suspect my father is an Aspie himself. Mom says to me about certain things "Don't get your father all wound up"
Also, aside from that. Has your bf had a history of being bullied? May be another part of his past that he can't let go and maybe some of the people you were with have bullied him before. Is there a chance that happened?