Per my divorce decree my ex husband and I were to split college education for our son 50/50. I have paid for all college expenses.

While there can be no legal advise given to you, we can suggest the starting point being your divorce decree.  It should set out what each parent's responsibility is regarding college. The divorce statute also contains specific language regarding contribution to college expenses. As to your decree, it may be that there is language that requires action prior to any expenses being incurred.  It is also possible that it is silent as to when such expenses are to be paid.  If there is a 50/50 obligation, one would hope that you could petition the court for reimbursement of the monies paid.  It would then be up to the court to review the matter.  You may be able to seek monies for all 5 years or only the first 4 years. The suggestion is for you to secure documentation detailing all monies paid by you for college.  Also, any letters or notices to the father over enrollment choices, expenses, grades, etc, should be gathered as well.  These materials, along with copies of grades obtained should then be taken to an attorney experienced in such post decree matters.  The attorney should be able to review all of your materials in light of both the decree and statute and make an assessment as to the likelihood of your recovery and what limitations, if any, you should expect from the court. You should do this sooner rather than later.