Can you explain the concept of an annulment of marriage in the Roman Catholic Church and its effects on a previous marriage?

It’s a bit complex if you don’t know the Theology behind it but basically, Matrimony is a Sacrament in the Catholic Church. In many countries, the Sacramental ceremony is separate from the Civil marriage. As a Sacrament, it is a solemn vow before God and witnesses that you are entering willingly into this union and intend to remain for the rest of your life. If you have a Civil marriage as well, and in many places the Sacrament and Civil ceremonies are the same, you will still need a Civil divorce to determine support, child custody, division of property, etc. but it in no way frees you from your Sacred Vows. You are still married in the eyes of the Church and may not remarry. Living with or even just having sex with another is considered the grave sin of adultery.

If one Catholic spouse files for a Decree of Nulllity, it is essentially a court proceeding and proof is needed that the vows were somehow invalid. My ex-husband did this but he took it upon himself to confess that he had taken his vows in vain at our wedding. He admitted he had no concept of what marriage entailed and that he didn’t want to do it but went thru with it for appearances sake. the Decree was granted and he remarried in the Church. I also remarried but I had left Catholicism and did not marry in the Church. My “husband” died 3.5 years ago and I have returned to Catholicism. I had to go to Confession and receive absolution for living in sin with him because while the marriage was recognized by the civil authorities, it was not in the Church and not Sacramental. However, had I chosen to return to the Church 36 years ago, I would have been free to marry him in the Church ( he was Christian but not Catholic) because my daughter’s father took the correct step of getting the Annulment.