I found this video out on YouTube. It is rather well done in articulating the Church Teaching against “Same-Sex Marriage.” It is sensitively done as well, making clear that the Church does not reject or “hate” individuals with homosexual orientation. Yet to speak the truth in love means that we must insist on abstinence from sex for all unmarried individuals. Further, we cannot depart from Biblical teaching on the nature and purpose of marriage. We must remain consistent with Biblical truth and the constant teaching of the Church. It is a rather brief video and I recommend you view it and share the link with others.
Bottom line is, God has established marriage as a stable, lasting union of a man and a women and oriented it to the pro-creation and rearing of children. I have often quoted Genesis 2 and 3 in this regard but, here is another quote from the book of Malachi 2:15-17:
15 Has not the LORD made them one? In flesh and spirit they are his. And why one? Because he was seeking godly offspring. So guard yourself in your spirit, and do not break faith with the wife of your youth. 16 “I hate divorce,” says the LORD God of Israel, “and I hate a man’s covering himself with violence as well as with his garment,” says the LORD Almighty. So guard yourself in your spirit, and do not break faith.
Here then is the video