How many of you all actually remain friends with your exes? But well, first it really depends how it ended. Sometimes these exes become your best friends, because think about it, you have a history with these people, you shared maybe a brief or a long period of your life with them, he/she probably knows you inside out.
It's quite a different story when you have a current other half though. How then do you deal with the exes? Current other halfs might not understand why you're still close with your exes. But really there's nothing wrong to me anyways. What's wrong with being friends? Ultimately is to keep an open mind.