Coping with the Ex!

Often times within a relationship, just as long as both parents are together then everything is peaches and cream and each parent plays their role. Once the relationship ends typically the father bails out and no longer has a sense of responsibility while the mother is left to be mother and father which then her anger turns into bitterness and unforgiveness. Should parenting stop once the relationship is over? Should child support be enforced? If you were in this situation what would you do?