Not-so-instant recognition

Last night I passed a guy on the street who I lived with for a year - 10 years ago. We did the whole "I know that person, why do I know that person?" stare but ultimately didn't acknowledge each other. Now I'm a bit freaked out by the whole thing.

This was not just a roommate, this was a relationship - and a long one. I don't know what freaks me out the most: that it would seem he did not get to the recognition stage; that it took me as long as it did to recognize someone who once was incredibly significant to me; or.... that once I thought about it, I realized that sufficient time had passed for both of these things to make sense. (And we ARE on the other side of the country - what are the odds?)

I suppose he could be asking himself these same questions today... who knows? Or maybe now it'll be blue car syndrome and I'll run into him everywhere. Again - what are the odds?