I've never been able to manage this. Once I'm "in love" and it goes sour, I usually need a LOT of distance from the person to even begin the process of getting over it (no matter who pulled the plug), and at that point, we've grown so far apart that interaction in the future is awkward. That's best case scenario, too … sometimes, old feelings get kicked up, which is even worse.
I'm always a little perplexed by people who talk about hanging out with exes as friends long after relationships are over, but I've noticed that the people who say that they can do this are the sort of people that have very high relationship turnover (the folks who can point to a long list of exes, and always seem to be "with" somebody, never single for longer than a month or two).
The only thing I can think is that their definition of being "in love" is very different from mine. Love, for me, is drowning in the concept of somebody, and if it goes on long enough, making them a secure fixture in your life. Comfortable and known and reliable. They should never stop making you happy when you get to spend time with them. I don't even cross into the "relationship" zone with them unless I'm literally getting butterflies in the stomach when I think about them.
Others just go "meh" and say "let's see how it goes" and slap that Facebook In-a-Relationship status up at the drop of a hat.
The people who have exes as friends never give themselves over to it as completely as the people who can't be friends with exes do. They're holding parts of themselves back, always guarded, so that they never risk becoming too invested. That's my theory.
