The Supreme court in Windsor v US stated that the states...not the federal government had the historical authority to define and regulate marriage. The ruling also established that the states could not violate the rights of their resident in doing so.
So lets recap. Federal government ruled not to have a historical right to regulate marriage in Windsor and DOMA.
States do have the right to regulate marriage based on historical precedent...and states although have the right to regulate, do not have the right to violate the rights of their residents in the applications of their rules...[14th].
That will be the judicial reasoning used in the court to affirm that states can not ban SS couples from marring and by violating their equal protections under the law..