I am friends (such as it is) with my ex cuz we have a daughter together. Not friends in the sense that we hang out or whatnot... but he does not bother me any more...
BUT the thing for me is that there has to be time and distance. I have to be in the position of really honestly not being in love with them. If there is any chance that I still have feelings I can not be around that person.... it hurts too much.
First priority is YOU..... if it hurts dont do it.