That's the fear that some people have – right? Some Christians say, "It won't ruin my marriage, exactly, but marriage in general, and the family specifically will be torn apart if homosexuals are allowed marital rights."
Truth is, the fact that we've arrived at a place where homosexual marriage is even being talked about in the way that it is means that marriage, as it was meant to be, is already ruined. It was ruined way back when common-law relationships were considered equal to marriage as instituted by our Creator. In fact by the time they're 39 years old, 60% of women will have lived in a common-law relationship. That's something when you think that prior to 1960, almost no one, only those on the criminal / addiction fringes lived common-law.
What we have before us today is a generation of children who know nothing of the kind of love that makes life-long commitment to a relationship possible.
All mammals, including humans, learn relationship by what they see while growing up. Deny those essential observations and you've emotionally and relationally handicapped that offspring for life.
Because we've turned our backs on Jesus ("The one who loves Me is the one who will obey Me."), we've ordained temporary arrangements that are built on “Can you make me happy,” the standard by which we determine “love.”
We've sown the wind and we will indeed reap a whirlwind.