Marriage is a topic which is widely discussed today.
As God has ordained it, it is between one man and one woman for life. When two persons are validly married, the marriage only ends with the death of one of the spouses. It cannot end in a divorce. Even if a person gets a civil divorce, they are still married to their spouse until one dies.
No Divorce in the Bible
Jesus clearly taught this truth to his disciples and the crowds. “Have you not read that the one who made them at 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 flesh’? So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate." - Matthew 19: 4 – 6. The Pharisees ask Jesus if divorce is acceptable, since Moses allowed it, and Jesus clearly responds that it is not. God's work of joining together in marriage cannot be undone by human beings. St. Paul also reiterates this teaching. "To the married I give charge, not I but the Lord, that the wife should not separate from her husband (but if she does, let her remain single or else be reconciled to her husband) and that the husband should not divorce his wife." - 1 Corinthians 7: 10 – 11. Even 2000 years ago, divorce existed and was well-known, but Jesus, and St. Paul in accordance with Jesus, condemns divorce. As St. Paul teaches, if a married couple is divorced in the eyes of the law, they must remain single, for they are still married int he eyes of God.
No Divorce Early Church Fathers
The early church fathers also taught that divorce was wrong, and to remarry after a divorce is to commit adultery.
Just as a woman is an adulteress, even though she seem to be married to a man, while a former husband yet lives, so also the man who seems to marry her who has been divorced does not marry her, but, according to the declaration of our Savior, he commits adultery with her – Origen Commentaries on Matthew 14:24
No one is permitted to know a woman other than his wife. The marital right is given you for this reason: lest you fall into the snare and sin with a strange woman. ‘If you are bound to a wife do not seek a divorce’; for you are not permitted, while your wife lives, to marry another. - Ambrose Abraham1:7:59
According to our teacher, just as they are sinners who contract a second marriage, even though it is in accord with human law, so also are they sinners who look with lustful desires at a woman. He repudiates not only one who actually commits adultery, but even one who wishes to do so; for not only our actions are manifest to God, but even our thoughts. - Justin Martyr First Apology 15
Wherever there is fornication and a suspicion of fornication a wife is freely dismissed. Because it is always possible that someone may calumniate the innocent and, for the sake of a second joining in marriage, act in criminal fashion against the first, it is commanded that when the first wife is dismissed a second may not be taken while the first lives. - Jerome Commentaries on Matthew 3:19:9
These early Christian authors clearly taught that taking a second wife while the first one is still alive, even if a divorce has been finalized, is wrong and the sin of adultery. Their understanding of the permanence of marriage is in line with what the Church has always taught about this important sacrament.