So you're worried and feeling quilty because you're not as excited and happy for your friend and her second baby than you were for the first? I'd say that's normal; new things can be very exciting, and while babies aren't "things", the same applies to them. Parents are usually very happy about the second kid too, but for others it's not such a special case anymore when there already is one.
It's also common that friends who have kids and friends who don't drift apart a little; I wouldn't call it an aspie thing. You can still hang out, though it's likely that the kids will often be there too. When they're a bit older, you might actually have some alone time together, too. Try not to stress too much about the situation and enjoy your company with your friend when you can. If you're able to, try to subtly direct the conversation to something else than the babies from time to time. Not always, but sometimes.