If you are divorced with a divorce decree and the ex-spouse won''t exchange tax rtns to determine if child support should change what should I do?

His paying for all expense previously does not necessarily mean that he is required to continue doing so if he is/was not required to.  So, to answer question 1. In general, and without know the exact facts,  you can get it in writing if he agrees to put it in writing or if the child support calculation based on your incomes and division of expenses requires him to pay all expenses.  2. If he previously paid all expenses, there is really no relevance to his prior tax returns.  Regardless, you cannot retroactively modify child support.  Child support is modified as of the day you file a motion to modify child support, if such modification is awarded.  You can find basic forms on the Colorado Court's website under "Forms" "Domestic/Family."  Click here to go to the link.  Additionally, you should know that he cannot necessarily claim any extra payments he made over his required child support payment as additional child support payments (i.e. to offset future payments).  I suggest you discuss your situation with an attorney to determine the best course of action for your specific situation.