Well, I myself think it's ok to just not have a friend. When I say 'friend' I mean people who I can talk and trust, not the many people who I talk just for getting an information or any other purpose. I think you say 'friend' meaning the same thing than I mean. It's very good to have a friend, as we may know, but it happens that aspies experience some difficulties making friends, leaving it ok to not having a friend.
However, before thinking that your only friend isn't your friend anymore, make sure that he made new real friends, not the friends many people mean, just companies for parties. He might be temporarily trying a new world of clubs and parties and he may notice that this isn't a cool environment as it may seem. If he goes back to the down to earth person you described, he will probably find that you are a real friend of him.
It's sad to lose a friendship. Try not to do so.
_________________
I'm not a native speaker of English. Sorry for any mistakes commited
