Marriage

I am not a well thorough educated debater about the issue of marriage. But from my common sense and just what I do believe a marriage is a union between a man and a woman which is instituted by Christ.
Now, in this generation the marriage between a man and a woman is now being REDIFINED! What the heck is that? Where does this thinking came from? I am not against homosexual as what the bible says love the sinners hate the sin, but they won't commit sin just being a homosexual but when they do an action that is beyonddddd. But then redifining the meaning of marriage is off to me.