
The teaching of Jesus in the New Testament is against divorce (the legal ending of a marriage before the death of a spouse).
It was also said, ‘Whoever divorces his wife, let him give her a certificate of divorce.’ But I say to you that anyone who divorces his wife, except on the ground of unchastity, causes her to commit adultery; and whoever marries a divorced woman commits adultery.
Matthew 5:31-32
Adultery (sex with someone who you are not married to) is also wrong according to the teachings of the Ten Commandments:
You shall not commit adultery.
Exodus 20:14
Many churches now allow divorce but a marriage can only be ended by an annulment in the Roman Catholic Church. This means that the marriage is regarded as never having taken place for special reasons.

Christian couple on their wedding day
In 1981 the Church of England allowed people to marry again after a divorce. Many other churches now hold this position.
The Roman Catholic Church is totally opposed to people cohabiting (living together without being married). Sexual intercourse outside of a marriage is a serious sin [Sin: Act of rebellion or disobedience against the known will of God. ] and couples who sin in this way cannot receive communion in church. Some Protestant churches accept cohabitation although they hope that the couple will choose eventually to be married in church.