Go back and file an order to show cause to modify custody. Depending on how far away your mediation appointment is, you may be able to tackle both situations in one appointment. Let the judge decide whether he is willing to modify custody, however, if you willingly terminate your employment, you will still be responsible for your legal obligations and how depressed do you think you will be once you are hauled in for contempt?
You need to get medical help, possibly some medication and pick yourself up by the bootstraps. If you need help with the court issues, visit your local Family Law Facilitator there is one in every courthouse that deals with family law issues. They'll help you do the paperwork, but they won't represent you.
I do take issue with one thing you said though... a parent that willfully withholds their children from another parent is NOT a good parent that loves their kids. They are selfish.

