I've always been an advocate for and practitioner of the 'Clean Break Policy' when it comes to break-ups. Most (but certainly not all) of my break-ups have been amicable, but there is always some level of pain involved, and cutting an ex out of your life is the most effective way to start the process of moving on and healing.
To keep an ex in your life is like allowingn a wound to remain open and to fester, not scab over and never allows the healing process to begin; or at the very least, slows it down significantly. I only ever saw one friend who genuinely managed to become/remain proper friends with an ex, and even then, they still had a falling out a few years later.
I can completely understand that this could be impossible in situations with divorce and where kids are involved, but even then, contact should be limited to business pertinent to the children only. But of course, keep it polite!
Fighting the Good Fight...