Most Helpful Guys
If you can't understand it at all, you may don't understand my answer. A relationship can transform. A meaningful romantic relation can become a strong friendship once both realize they have more in common as friends than a couple. Sure, you can be friendly with your ex and your ex may rather maintain distance. It depends on everyone personal view of what should happen after a breakup.
Most Helpful Girls
Not everyone ends relationships in bad terms. Sometimes if the break up is not ugly, but it's more like both of them realize together that it won't work and they need to move on, they can agree to be just friends
I can understand in situations where it never got serious. Like they gave it a try cause they liked each other, but it wasn't romantic. But it could sabotage future relationships as jealousy is natural.