Well, it's normal for two people to evolve differently - after all, they're different people
Maybe you'll feel better about it if you ask her what passing the infatuated phase actually means to her - she thinks about you less? She can actually do her homework without constantly daydreaming about you? Her answer will most likely *not* feel threatening to you, and you may feel better if you find out.
It's positive because it means you're over the "newness" of it, and you're more settled in together. I see that as being a good thing.
It's kind of like going on vacation. You get somehere, and it's awesome. The hotel is amazing and the skiing is great, or whatever. After a few days, though, you've settled in, and you know the slopes better and you're a bit used to it now.
The downside is that it's not all new, new, new anymore. The upside is that you know some of the slopes and runs quite well, and maybe you're comfortable enough try some harder runs, or take a day off skiing and sit in the hot tub.
It's not better one way or the other - it's a tradeoff: giddiness for relaxation?
OK, that wasn't a great analogy, but I hope you get my point
Hope this helps,