That’s pretty relevant to your situation here. I work in mental health, and I’m sure you’re likely already aware of this but- this sort of thing is very common with BPD, and is actually on the tamer end of what partners of pwBPD tend to go through.

It’s clear you really care about him so I won’t start with any “run for the hills” stuff, but I recommend seeking resources for people in your position. There’s a subbreddit for partners of pwBPD I’ve heard is helpful. Best of luck to you both.

First, you clearly care a lot about your boyfriend’s happiness and emotional security, and I think that’s awesome. I’m sure the hurt for him is real, regardless of whether it’s rational.

That said, this is a pretty common thing for couples to comment on. I don’t think you missed any social cues due to ASD in this instance, most people wouldn’t think this is a big transgression, if a transgression at all. It’s one thing to say you think someone you actually know is hot, that could justifiably lead to some insecurity. Talking about celebrity crushes just isn’t the same. My wife and I are totally monogamous, but it doesn’t bother me hearing her drool over Henry Cavill, and she doesn’t mind me drooling over Christina Ricci. It’s just silly crush stuff, not real.

I hope he can get some help with this and work through it.