a running friendship
I'm not a runner, and I don't have any friendships based on running, but I'd be remiss if I didn't point you to Sara Corbett's new piece in Runner's World, Someone to Run With.
Any friendship that is based on running is, in essence, about accrual -- of time, of miles, of intimacy built over a lot of small steps forward. It sneaks up on you that way, I think. It can seem merely enjoyable until you need it for more.
Worth reading in full, especially for the lovingly run-on description of her friend Clare. (I won't ruin it for you, go read it in context.) If Corbett's name seems familiar it's probably because you've spent hours with her on the weekends: she's a a contributing writer to the Sunday Magazine in the New York Times. This past April had a long piece there on cellphones and global poverty.