Child support obligations often end when the child turns 18 and becomes emancipated, meaning the child can support themselves. Since your ex is no longer supporting them, you no longer have to pay support either.
However, in some cases, a child who attends college is not considered self-supporting. College takes the place of work, but it does not come with an income or a living wage. The child may still live with your ex until he or she earns a degree and then becomes emancipated.
What this means is that the support obligations may not end, as you'd hoped. You may still have to pay until the child is done with school.
However, the cost may go down, depending on the specific situation. If your child lives with your ex and commutes to school, for instance, support will probably stay the same. If your child takes out loans for tuition and room and board, though, your obligations could decrease. After all, your child now lives at the school, which provides lodging, food and much more. This reduces the financial strain on your family, even when your child is paying for it with loans.
If you do think that your child support obligations need to be reduced for any reason, make sure you know exactly what legal steps to take. You do not want to make any reductions yourself or refuse to pay. You may need to have the court legally alter the support order. Always follow the order that is on file, even during this process and even if you feel that it is no longer fair.