This is a common outcome of situational friendships based on being in class together for instance or working with someone. People like to think those friendships will last even after the situation that brought them together ends but most don't so they give lip service to the idea that these people are actually lifelong friends by saying things like lets meet up with no real intention of doing so just in case they need the contact later for networking etc. Most people are lucky if they have one or two real friends for life but realistically speaking social groups change as circumstances do so keep up with this group as much as you want but get started on making new friends who are in sync with your life now. Good luck.