This prompt is fortuitous—monsoon season appears to have arrived in Manchester. Slate grey sky, leaky gutters, and dodging cars that drench you as they plough through puddles that could easily be mistaken for small lakes. Anyway, the wind chimes and gothic slabs of synthesiser combined with Robert Smith's world-weary vocals on Plainsong suit the despondent, resigned mood this weather puts me in.
This is a lovely, thought-provoking question. I think there must be at least one song—if not more—that reminds me of each old friend I'm still in touch with, people I could easily start a conversation with today. What's sadder are the songs that remind me of friends I've lost touch with over the years, people I seem unlikely to ever hear from again. Those hit harder as you travel further down the road.