Marriage comes from the loving hand of God, who fashioned both male and female in the divine image (see Gn 1:27).
A man "leaves his father and mother and clings to his wife, and the two of them become one body" (Gn 2:24).
The man recognizes the woman as "bone of my bones and flesh of my flesh" (Gn 2:23).
God blesses the man and woman and commands them to "be fertile and multiply" (Gn 1:28).
Jesus reiterates these teachings from Genesis, saying, "But from the beginning of creation, 'God made them male and female. For this reason a man shall leave his father and mother [and be joined to his wife], and the two shall become one flesh'" (Mk 10:6-8).
source: Between Man and Woman: Questions and Answers About Marriage and Same-Sex Unions | USCCB