Your ex may claim the education credit, even though you paid the expenses, since the student is his dependent.
You may claim the loan interest only if you co-signed the loan or it was a parent loan. The student does not need to be your dependent, this year, but must have been your dependent for the years the loan money was used to pay expenses. So, probably not.
Here's a new issue: If your child is emancipated (18 in almost all states), she is no longer considered to be in anybody's custody. So the special rules for divorced parents no longer apply. If the student normally lives with you, she is now only your "qualifying child" and the other parent cannot claim her, unless the qualifying relative rules apply (unlikely). That is, your divorce decree may no longer be valid, and you can claim her because she live with you. You may want to review this with your lawyer (I am not lawyer).
There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, student status, a relationship test and residence test.
See full dependent rules at: https://turbotax.intuit.com/tax-tools/tax-tips/Family/Rules-for-Claiming-a-Dependent-on-Your-Tax-Ret...
