Whether my co-worker and his partner are married or not (I honestly don't know if they are) has NO bearing on the quality of my marriage.
It's not so much that gay marriage will or will not have an effect on YOUR marriage or my marriage. It's that gay marriage will have an effect on "marriage" according to what marriage is supposed to be.
Gay marriage is as wrong morally and Biblically as open/swinging marriages, abusive marriages, getting-drunk-and-going-to-Vegas marriages and so on.
None of them are entered into via the model that God laid out for us to follow. Worse yet, 50% of those who quite possibly did enter into marriage the "traditional" way have called it quits at some point prior to "til death do us part", thereby reducing the holy commitment between 2 people to little more than hollow untruthful words.
It's because of this that we can look at a supposedly committed homosexual couple and say things like "if only heterosexual couples would act like them..."
Yeah, you go on and use a homosexual couple as the basis for how things should be.
God wouldn't mind, right? Maybe He's looking for a new moral standard, seeing as how we can't live up to the one He previously gave us...
In some ways I welcome all of this mess. It simply means that we're getting that much closer to Jesus' return. And how surprising it will be for those "Christians" who will think nothing of taking a mark on their right hand or forehead, just because it will have no bearing on their quality of life...