Marriage between a man and a woman was instituted by God with Adam and Eve. Genesis 2:24 states: “Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh”.
In Matthew 19:4-5 we see Jesus reaffirming this: “He answered, ‘Have you not read that he who made them from the beginning made them male and female, and said, `For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one’?’”.