1 Corinthians 6:16-18

Do you not know that the one who joins himself to a prostitute is one body with her? For He says, “THE TWO SHALL BE ONE FLESH.” [Gen 2:24] But the one who is united and joined to the Lord is one spirit with Him. Run away from sexual immorality [in any form, whether thought or behavior, whether visual or written]. Every other sin that a man commits is outside the body, but the one who is sexually immoral sins against his own body.