I am legally separated from my husband. Is it a breach of contract if he moves to New York from South Carolina, which SC is where I live with our kids

It sounds like there are two potential grounds to argue that he should have less visitation due to a material change in circumstances.  First, he moved to another state.  Now, at least in Maryland, whether a move to another state constitutes a material change in circumstances depends largely on the extent and frequency of the moving parent's custody rights.  For instance, if he was only granted reasonable visitation from time to time as agreed, then the move would probably not constitute a material change since it does not prevent the visitation schedule from being carried out.  On the other hand, if he was granted extensive visitation (i.e., shared physical custody or every other weekend plus two or three weekdays each week), then the move would almost definitely constitute a material change in circumstances, since it was from South Carolina to New York. More concerning is the fact that he no longer seems to have an interest in his visitation.  Since his absence has been continuous for more than six months, you could probably successfully argue that a material change in circumstances (he no longer has an interest in the child's life) has occurred.  Whether this is worth pursuing again depends on how much visitation he has to lose.  If he has extensive visitation rights, you should move for a modification; if he has the bear minimum visitation already, then it would make no sense to file for a modification. In sum, if he has extensive visitation rights, then you have good reasons to consult with a Child Custody Lawyer.  I am only licensed to practice in Maryland, so you would need to contact a lawyer licensed in your state.