What does Church teach about Divorce?
The short answer is that divorce should not exist according, not just to the Catholic Church, but from the words of Christ on marriage. “Anyone who divorces his wife and marries another woman commits adultery.”Matt 19:9 (all three synoptic Gospels mention this teaching)
However, the Catholic Church, under the guidance of the Holy Spirit, does not look at divorce just as a legal matter, but as a sacramental one. A valid Catholic marriage must be entered into freely, faithfully, be open to life and with the expectance of permanence! If these elements are not present at the time the marriage takes place, the marriage itself may not be a valid sacramental union. (This is what the tribunal will look at if considering annulment.)
But it is important to note, that there are other choices besides annulment. Living a chaste life, outside of another relationship, is a choice. Even separating (possibly legally divorcing), but continuing to live out your marriage vows (though separate) is another choice.