There is no sound rules about Ex's, if they all came with directions it would help. I do know that you cannot have a partial relationship. You are either in or out, but that doesn't turn off the feelings.
I still love my first fiance, but it is not the same intensity as my current mate. I think if you are really close you either end up hating them or having some heart twinges. That's why divorce is so bitter.
My only hard and fast rule, and it doesn't apply here is that kids are not weapons!