He may be able to get the child support amount reduced if he is now earning significantly less than when the support amount was first established. He cannot, however, reduce it just based on the fact that he is now supporting another child.
Children born subsequent to a child subject to a child support order are not a reason to lower the child support order in place. However, if his income has decreased since the child support was ordered, he may be able to file for a modification. If that is not the case, a modification would be difficult. His expenses do not factor into the child support guidelines.
You should consult an attorney regarding your individual situation because every case is different. The answer I provided is based on limited facts, and should not be construed as an attorney-client relationship. if you would like to set up a consultation, please call our offices at (407) 894-1122.
Child support is based on your fiance's income. The fact that she has less household expenses than your fiance is not relevant to a determination of child support, sorry. But keep in mind his financial difficulties may be relevant if he falls behind in child support and a Contempt Motion is filed--he may have an argument that he is not in willful violation of his requirement to pay the court-ordered amount, though he will likely still have to live with the requirement to pay it.
Unfortunately, the answers provided by the other attorneys are correct. In Florida, an afterborn child cannot be used as a basis, in and of itself, for lowering your child support obligation. Right or wrong, the rationale is that your fiance knew about the first childwhen he decided to have a second, and in Florida the first born child, barrring extraordinary circmstances, has the first right to support. On the bright side (if there is a bright side), if the mother of the older child ever tries to increase child support in the future, the Court will take your child with your fiance into account in whether an increase would be warranted.
Family law rules differ significantly in every state, especially procedural rules. Always seek the advice of an attorney in the state where your divorce was filed.