Either it's just me - and I don't think it is - or we all compartmentalise our lives, our friends, our relationships. I have friends - sometimes just one, sometimes a group - from Uni, Lincoln, Law School, London, Home (work) and so on and so on.
It is like a big complicated venn diagram. Lots of people know each other, lots of people have never met (and probably wouldn't get on), some people have lots in common, some people have literally nothing but you in common. Over the years, the diagram drifts, changes, sometimes quickly, sometimes at a glacial rate, imperceptibly slowly.
Some friendships have a natural shelf life, but some are too strong to really die even after 15 years of not being in contact, they are just...latent. A time like this is the acid test of those relationships - you quickly realise that there are some people who are important to you - and you to them - that it's great to be back in touch with, great to hear from. Their voices, either on the phone or on email, are unmistakeable.
But really, aren't we silly for letting these people drift out of our lives in the first place.
