He apparently based it on the State Constitution's equal protection clause, in an effort to avoid federal review.
This is where they artificially construct "classes" in order to abuse the concept of Equal Protection.
Marriage is by definition a legal union between a man and a woman. Nothing else. Sexual preference is none of the states business nor is it part of the state's contract. Regardless of their "sexual preference" two people of the opposite sex may not marry each other. And regardless of their sexual preference, those same people are legally entitled to marry someone of the opposite sex.
It is perfectly equal unless you accept the bizarre notion that the state can define new classes of citizens based upon something as personal and legally unprovable as sexual preference.
No different than the queer judicature, who is benefiting from all of these personal decisions?