I guess it helps to have Catholic Priests in the family.
According to the Catechism of the Catholic Church, 2nd edition:
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.
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It can be argued that the alcoholic has abandoned the marriage, in which case there may be a case for an annulment. Such decisions are made on a case to case basis by a Church tribunal. It also
depends on which of the 27 or so Catholic rites you belong to. Some are more flexible while others are stricter.