ex. wife moving out of state with kids

Child support is based upon specific calculations that essentially work out to 17% of your boyfriend's adjusted gross income.  So the fact that she will have free rent does not mean he can ask for lower child support, since the calculations will still remain the same.  However, if he's paying child care expenses, that may decrease depending on her job situation.   In terms of travel, your boyfriend and his ex-wife will have to come to some formalized agreement about what the new visitation schedule will be.  Specifically, how often he will see the children, and whether he will always be required to travel to the children to have visitation.  But they should at least write out some formal agreement so that if the circumstances are such that the burden will be placed soley on your boyfriend for all travel and expenses, then he will have proof of their agreement in any motion for downard modification of child support.