Ferret, reading your post reminded me of some situations in my
life too.
I've lost a few close friends through 'natural attrition' too. When
my electronic phonebook conked out once, taking along with it to
the grave all my friends' contact no.s, I was beside myself! I was
mourning over the loss of all the contact no.s - how was I going to
call up my friends?! 
And then I realised something... if they missed me and were
thinking of me too, they would call me. Which a handful did, the
rest never did.
I guess friends are like those little paper boats with candles
inside that the Thai's put out in the river during one of their
festivals... some of the boats would float out into the ocean and
never return, other paper boats would always float pretty close to
shore and remain within your range of vision always.
As we go on in life, inevitably, we keep some, we lose some. Not to
forget, there will always be new paper boats that'll come and berth
in our docks, be it for a short while only or for a long, long
time.
I've learnt to look back and smile at the happy memories. I no
longer question why or think about the what-could-have-been's.
Friends come, friends go, and there will always be that special few
who'll stay on and make their home in our hearts. 
