Have you noticed that segments of your social circle seem to be breaking off into smaller units? You can try to figure out why this is happening, but what is the point? Reshuffling happens all the time, and it's usually a very organic and necessary process. If you get caught up in who's spending more time with whom, you are really going to drive yourself crazy! Just be happy that so-and-so is getting to know so-and-so better, and leave it alone. Everyone will be back together soon.