Like most have said, you can lose track of your mates from school.
I look back on those times as important and I guess formative years. Finding out about cars, girls, booze and whatever else.
Anyway, point is, I recently set about re-connecting with the guys from school. We have found a group of maybe 15-20 of us that get together every few months . . . a pub in the rocks, Lidcombe oval, or a restaurant somewhere. Some of us hadn't seen each other for 40 years. It's good for your soul to rekindle the laughs you had during your school years and re-connect.
One thing I have found out about friends is that your real friends . . . the 3 or 4 that are long term . . . it doesn't matter if life gets in the way and you don't see each other for a few months or more . . . when you get back together it picks up straight away, as if you saw each other a few weeks ago. No judgement, no criticism about who's turn it is to call . . . it just carries on seamlessly.