<p>You mentioned that the ex husband has a new wife and three other children, is that correct? It might be harder for him to come up with the same amount to contribute to your daughter’s college costs. Also I don’t know if parent can claim AOTC for a dependent who is not listed on tax return. So if that is the case and you end up paying more, maybe you can agree for you to claim her for these four years.
Ex would miss out on the exemption, but with three other children his tax liability should not be that different.
You could get the exemption and with the tax credit that might offset any higher contribution on your part.</p>