I'm happy and all that but what should I expect? I hear lots of people say they lose their best friends when they get married. I like his girlfriend just fine so I think I can stay friends with them but I'm worried. Since I'm single especially I can't imagine what sort of things we can do together anymore.
Well the time you spent with him will reduce but he can't cut you out completely. And also you can ask him and his wife to help find a girl, I am sure they will be more than willing to.
It's over. Don't bother them. You should know what to expect. We can always be there as friends, but their priority now lies with their spouses. Keep a relationship with them as a PAIR. It's safe to treat them now as one person, since there's nothing they will keep from each other. So try to know more the spouse and get to do fun things in group. (Always keep the possibility they will try to find you a partner as well.)