Marriage has civil and ecclessial dimensions. States can recognize it, and churches can sanction it, but a marriage is not founded upon either. The Creator instituted marriage in Eden, and a marriage is properly enacted in the mutual commitment between a man and a woman.
However --legal or not--, as with divorce and extra-marital sex, homosexuality is not only destructive to society it is also destructive to individual persons.
I recently attended a presentation by the Baltimore- D.C. area Regeneration Ministries. They are a member of Exodus International, a worldwide network of services to people overcoming homosexuality. I recommend them to anyone with sexually related struggles, and to those who want to learn more about homosexuality and how to help homosexuals.
I also recommend this informative book by Orthodox Presbyterian pastor Charles McIlhenny.