I just had this experience happen to me this past spring. Ex and I were growing apart, we've become completely different people over our realtionship it wasn't the first time I thought about ending it. Being in school we have some mutual acquaintances as we came to find out that many of our friends share programs. We broke up, and a couple of weeks later she was texting asking if we could still hook up NSA, well it doesn't work that way. So randomly for the next couple of months I would get a text from her asking how I was doing, or she would enlighten me on the stupidest thing that she stumbled across while studying, this is something we got into the habit of doing while dating as it usually amused both of us. After I would not reply to such attempts at trying to restart a relationship she would send a bunch of texts summed up with "I'm so unhappy we're not together anymore, can we please give it another go?" (+More issues than I hadn't realized during the relationship). Then about 3 months after the break up, she finds me on campus, sits down at the desk I'm working at, stares me dead in the eye and says " I know that I fucked up and was a horrible girlfriend, but you weren't prince charming either. So let's give this a second go round, okay" I replied with a flat, no, and told her to leave me to my assignment as I came into the library to avoid distractions. That weekend I got a text from a friend of mine asking permission if he could have a crack at her... Go right ahead. (He and I are very similar personality wise, and she knew him before) I get a text the next morning telling me that my ex flat out propositioned my friend (prompting the text). Then once it was over she began to ball her eyes out telling my friend that she missed me so much and would do anything to get me back. To sum up the story I don't say friends with ex's, I find it makes it awkard, especially if they are not over you (99% of the time there is more to the situation then meets the eye) or vice versa. Like Matt said it can and will screw up the potential for future partners.