Marriage is sacred and holy, because God instituted marriage, not man. There are many perversions of what God intended in marriage: adultery, homosexuality, incest, fornication, lewdness, pornography, etc.
What does God think of adultery? In Genesis chapter 20 Abraham had journeyed to Gerar. Abimelech king of Gerar sent and took Sarah as a wife, because Abraham had said that she was his sister. In Genesis 20:3 we read, "But God came to Abimilech in a dream by night, and said to him, ‘Indeed you are a dead man because the woman you have taken, for she is a man’s wife’." Even though Abimilech had innocently taken Sarah, not knowing that she was Abraham’s wife, God almost struck him dead. God told Abimilech, "YOU ARE A DEAD MAN". Here we see God’s wrath being stirred up because Abimilech was about to commit adultery.
Can an adulterer go to heaven? In 1 Corinthians 6:9-11 we read, "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived, neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites….will inherit the kingdom of God. And such were some of you." This is a great price for an adulterer to pay by being lost in the burning fires of eternal Hell. An adulterer can repent. Notice again verse 11, "And such were some of you". Some of the Corinthians Christians were at one time adulterers before they became Christians, but they apparently had repented and were forgiven. They had given up their adulterous relationships.
The word "adultery" comes from "adulterate" which means "to pollute by adding a foreign substance." Adultery can be committed by having an extramarital affair or "whoever divorces his wife and marries another commits adultery" (Luke 16:18). If one continues in his adultery, he will meet the wrath of God. As we read in Hebrews 13:4, "Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge." Do people really realize how serious the judgment will be? In Proverbs 6:32 we read, "Whoever commits adultery with a woman lacks understanding; He who does so destroys his own soul." Let’s not destroy our souls.