I graduated in 2000, and since I've already started running into former students of mine at the bar, I'm considering myself one of the older posters on CCS....
My closest (I don't think 29 year old people should refer to others as their 'best' friends - just my thing, I could be wrong) friend is from high school. Actually, my closest friend and I have been friends since little league when we were 9. Of the other friends I hang out with they are all from high school. Not necessarily that I hung out with them in high school, but we've become better friends since.
Of my closest friends in high school, one got heavily into drugs and is probably living in a ditch somewhere. One teaches in Michigan, the other is a doctor in Miami, and the last one is a Senior VP for some tech firm out in California. Those were my closest friends, and obviously we all took somewhat different paths.
It just happens. Nothing to regret. You stay up on what they are doing through facebook, but other than that, it's not exactly like I can just get on a plane to Miami and inconvenience my buddy who works a hectic schedule in a hospital.