Being fair to your ex is the best insurance on a positive outcome for yourself, especially when children are involved.  Your well-being is actually helpful to the other because the happier you are the more likely you will be to treat them kindly.  Motives become multiple when you realize the best way to help yourself is to lift another.  


Concern for others is the basis of morality in all major religions, key to personal happiness and salvation.  


Secular traditions use different arguments to arrive at similar conclusions on the personal benefit of being considerate to others.  For example, Aristotle’s elegant ethical system took for granted that character, wisdom and happiness could only flower in the context of community. We are social creatures who grow by trial and error in relations with others while remaining true to needs of the self.  


All modern, Liberal Democracies are founded on an ethic of “enlightened self-interest” whereby individuals co-operate in seeking a maximum of pleasure over pain.  This can only be done by placing long term well-being above immediate gratification.  We co-operate and seek social harmony, recognizing that harming others places us at the greatest risk of being harmed in return. 


Self-interest can be both ethical and beneficial to others since we are bound in such complex social networks.   This the basis for a non-adversarial divorce since after separation you will continue to be connected as parents of the same children.  Your interests and the interests of your children will best be served when you and your ex-treat each other with respect.