In the early 70’s when civil law changed (by state), Civil divorce was granted even though one of the spouses did not want it. Before the early '70’s to get a divorce BOTH spouses had to agree to it. Up to the early '70’s, If you were Catholic and agreed to the divorce then you COULD NOT go to Communion, because you are in agreement of commiting a Mortal Sin (See below), “grave offense”
Malachi 2: 16 “For I hate divorce, says the LORD, the God of Israel”
In order to go to communion post '70’s you have to go to a priest to see if you are the “innocent party” in the divorce. If you are not the innocent party then you obtained a divorce wrongly and if you are truely sorry for your grave offence you return to your spouse where possible. Even separation (wrongly chosen, as with a man chasing other women or a women seeking a man who makes more money-it happens all the time) can be a grave offence since it is a form of abandonment and opens the door (as the catachism states) for temptation and further astrangement, rendering the situation “beyond repair”.
From the CCC
2384 Divorce is a grave offence against the natural law. It claims to break the contract, to which the spouses freely consented, to live with each other till death. Divorce does injury to the covenant of salvation, of which sacramental marriage is the sign. Contracting a new union, even if it is recognized by civil law, adds to the gravity of the rupture: the remarried spouse is then in a situation of public and permanent adultery:
If a husband, separated from his wife, approaches another woman, he is an adulterer because he makes that woman commit adultery, and the woman who lives with him is an adulteress, because she has drawn another’s husband to herself.
2385 Divorce is immoral also because it introduces disorder into the family and into society. This disorder brings grave harm to the deserted spouse, to children traumatized by the separation of their parents and often torn between them, and because of its contagious effect which makes it truly a plague on society.
2386 It can happen that one of the spouses is the innocent victim of a divorce decreed by civil law; this spouse therefore has not contravened the moral law. There is a considerable difference between a spouse who has sincerely tried to be faithful to the sacrament of marriage and is unjustly abandoned, and one who through his own grave fault destroys a canonically valid marriage