"The matrimonial covenant, by which a man and a woman establish between themselves a partnership of the whole of life, is by its nature ordered toward the good of the spouses and the procreation and education of offspring; this covenant between baptized persons has been raised by Christ the Lord to the dignity of a sacrament." 
(CCC 1601)

Marriage is a sacrament in the Catholic Church in which one man and one woman stand before God and His Church to profess their love and commitment to one another. On the day of the wedding, the couple promises three things to one another:

1. They intend that this marriage will last forever.
2. They will be faithful to one another.
3. They intend to bring life into their marriage through children.

Without these three elements being fully present when the couple is married, the sacrament of marriage is null and void.

The Lord Jesus insisted on the original intention of the Creator who willed that marriage be indissoluble. He abrogates the accommodations that had slipped into the old Law.
Between the baptized, "a ratified and consummated marriage cannot be dissolved by any human power or for any reason other than death."
(CCC 2382)

Unfortunately, however, all people are sinful. Not all marriages bring about the life-giving love that we are called to. This causes some couples to want to separate and/or marry someone else.

Most often this decision is not made lightly. It comes after many attempts to reconnect or heal the wounded marriage covenant, but to no avail. Civil divorce frequently acts as the "final straw" in a relationship.

In whatever way a couple may be feeling or experiencing, a civil divorce does not effect the truth that marriages are indissoluble. Should someone be civilly divorced and remarry, this second union is not considered to be a marriage.

We better describe an annulment as a Declaration of Invalidity. It does not deny that a real relationship existed, nor does it imply that the parties entered the relationship with ill will or moral fault. The Church is saying that the relationship fell short of at least one element necccesary to bring about what the Catholic Church understands as a true marriage.

(Diocese of Fargo, What is an Annulment?)

Children who are conceived or born of a valid or of a putative marriage are legitimate.
(Code of Canon Law, 137)

An annulment process has no bearing on the legitimacy of children. Children are always a gift from God. When a child is concieved an any marriage the that the couple presumes to be valid, the children are legitimate. 

If you or someone you know would like to pursue an annulment, contact your local priest. The annulment process can be a lengthy, and often painful. However, Our Lord is waiting to heal us in our brokenness. Divorces sadden Our Lord as much or more than it saddens us.

There is healing. There is help.