Anyone else out there feel bad about no longer being part of a group of friends?

No, not me. However i think back then you should've made your own new circle of friends, because it sounds to me like those "friends" you had were a bunch of spoiled and mean girls who all think alike. That's probably why they still ended up together - because they have the same way of thinking and they understand each other well. For now, you should take up a new hobby like painting or something, or you could focus on making new and better friends to make up for the ones before. This could keep your mind off your HS experience. Trust me, in a way, you're sorta lucky you let them go. Past is past, and for one, you could focus on achieving something great so they would be the ones to feel envious. ;)