This happened to me once. Summer after my sophomore year in college (2002) I spent the summer in St. Petersburg, Russia. I fell head over heels in love with a girl there, but of course had to leave in August to start the new school year back in the states. We vowed to stay in touch, but with 8,000 miles between us, it eventually faded.
In May of last year I was on my way home from Afghanistan and layed over in Almaty, Kazakhstan for two days of R&R (believe it or not, after Afghanistan, just about anything else is R&R). I decided to hit one of the bars, so I chose the one that looked the most happening. After I'd been in there for about 15 minutes, a girl comes up and taps me on the shoulder, and I turn around, and I'm sure you've already guessed by now, but it was her. She was getting a graduate degree at the local University of Economics. I literally didn't know what to say for what seemed like 20 minutes, as my brain was still going through the "Is this really happening?" phase. Seeing her again brought back a few things.