To secure and preserve the benefits of marriage for our society and for future generations of children, the union of one man and one woman in marriage shall be the only agreement recognized as a marriage or similar union for any purpose.
It's not all that different from the language in the second paragraph of SJR-7. It reads:
This Constitution or any other Indiana law may not be construed to require that marital status or the legal incidents of marriage be conferred upon unmarried couples or groups.
You can read the opinion here. A big hat tip to the Indiana Law Blog, which has more here.