During that logical marriage, I carried on a "friendship" with an ex-boyfriend for 12 years. Nothing sleazy was ever communicated, all of our behavior was exemplary, but that "friend" is the guy I now get into bed with every night. Really makes me re-think the whole "being friends with your ex" thing.
I also lost a friend that I'd been close with for 11 years when I was 23. We tried to date, lasted three months and crashed and burned spectacularly.