When I was fifteen, my life choices were shared with most of my friends. Which exams to sit, which boys to fancy, which jeans to wear etc. However, now we're 30, our lives are so varied and we all share so many different decisions. My old friendship group has been somewhat split down the middle; half of them are settled down and having babies, morgages and weddings. While the other half are living pretty much the same life as we were living five years ago.
I don't think it's just down to circumstance though. I imagine that even if I had a long term partner now, I wouldn't be looking to have a baby or a morgage, I just have a different life plan to that. It isn't just because I'm single that I am child free and a happy renter.
I guess that why it can be that so many school friendship groups just drift apart; our life paths just take so many different directions that we all end up pretty far away from each other.
Our priorities are not better or worse than each others', but can be so contrasting that a common ground can get harder and harder to find.