Will ex possible be the best friends of you?

I am not sure about that even though I ever thought of the possibility of it.

Some day I discussed with one of my pals and finally made a conclusion of the possibility of making ex best friends:

Case One: They were never, not really in love with each other.

Case Two: One of the ex is still in love with the other and he/she is willing to just stay with the other.

Case Three: They just want to keep close ’coz neither of them have made choices to the other.

Case Four: They are still in deep love with each other so that they want to keep the opportunity and possibility of their relationship.

Case Five: They were ever parents or they lived with each other for a long time. They look more like family than couple.

Sometimes it turns out to be possible but not necessary, while sometimes necessary but impossible.

For me, only case four and five sound the most reasonable for the possibility and necessary.