I think is a bad idea. One of the two always wants to come back. There is a reason for the break up. Also let's say there is no money, kids or common ownership of any kind so you are not forced to be friends. Also this take us back to the thread about if two straight people from the opposite sex can be friends it was a long debate but I think the general consensus was it is not possible. And now we add past emotional and sexual factors to this mix it becomes even more complicated. Also if someone says it is possible this has to come with real examples, perhaps your own and preferably with the opinion on both sides involved.