It's a really personal thing. Honestly, if he has it, it's up to him and him only, and it's not going to change anything.
With
sylvia1111's suggestion regarding speaking to a specialist, I know in the US it's illegal for specialists to do that to non-minors. And really, if someone did that to me, I'd get pissed off and they wouldn't be in my life anymore.
There are
so many things in the world. Maybe it's not AS and it's just his personality. I
do believe that that is how it is for some people.
But I feel like oftentimes that NTs try to find excuses for why their SO acts a certain way and wind up resorting to AS... it's more than what is on the outside and what one displays. Hopefully you've worked it out by now, but if not... maybe just let it go? It's up to him to realize it/acknowledge it/consider it/etc. We're not robots, thus there is no ON button to "trigger" our personal Aspie awareness.
(Like, people would often get mad at me for not accepting/realizing I have Bipolar Disorder... but I DON'T have it, and I
have been tested for it
three [separate] times. I found it and still find it very insulting when people continue to push it on me, especially when they don't know the story. Maybe you don't know the full story.

)