President of the Pontifical Council for Legislative Texts in the Roman Curia recommends an indisputable resource which specifies two acceptable reasons for spouses to stop living together.   First, when one's spouse is guilty of fault, and second, if one's spouse is ill with a contagious disease or severe mental illness making it unsafe to live together.   Whenever a spouse obtains a no-fault divorce,  the couple stops living together while the marriage bond still remains.  Divorced couples are truly still married (since they contracted to be married till death) but the civil system no longer recognizes them as having the status of married people. In civil no-fault divorce, the plaintiff simply abandons the dedicated spouse.

    The concept of malicious abandonment as a sufficient cause for separation is not expressly provided by current legislation. Its autonomous treatment and character regarding the other concepts of separation is the result of a work of jurisprudence and doctrine with the intent of specifically protecting compliance with every conjugal and family duty, penalizing their omission (3).
     It is differentiated from other causes of separation in that, while causes expressly defined in the CIC contemplate positive conduct —”occasions grave danger of soul or body to the other or to the children, or otherwise makes the common life unduly difficult”—, malicious abandonment contemplates noncompliance with every conjugal duty.
     Malicious abandonment is a negative situation or negative conduct of noncompliance with every conjugal duty. The party abandoning one’s spouse violates one’s matrimonial duties, that is, he or she fails to comply with the principle foedus nuptiale servandum est, because the spouse’s attitude consists precisely of a dissolution, in the sphere of social reality, of the conjugal consortium.  (excerpt from MTF publication. see full text below)

Canon law is written in Latin.  English translations with commentary are available.  In June 2004, the Midwest Theological Forum published an Exegetical Commentary of the Code of Canon Law: an 8-book, 8,000-page volume that includes exhaustive commentary on every canon and its original sources. The volume provides a literal “encyclopedia” to Canon Law.  His Eminence Julian Cardinal Herranz, President of the Pontifical Council for Legislative Texts in the Roman Curia, commented about this text: “Indeed, it would seem to me that this publication, carefully translated, clearly presented, and handsomely bound, will be an indisputable resource for English-speaking canonists, pastors, and students of the law.” (See quote in context)

The Pontifical Council for Legislative Texts is one of the departments of the Roman Curia.  In exercising supreme, full, and immediate power in the universal Church, the Pope makes use of the departments of the Roman Curia which, therefore, perform their duties in his name and with his authority for the good of the churches and in the service of the sacred pastors. (More Roman Curia)

Exegetical Commentary to the Code of Canon Law (©2004)

Canon 1153
§ 1. Si alteruter coniugum grave seu animi seu corporis periculum alteri aut proli facessat, vel aliter vitam communem nimis duram reddat, alteri legitimam praebet causam discedendi, decreto Ordinarii loci et, si periculum sit in mora, etiam propria auctoritate.
§ 2. In omnibus casibus, causa separationis cessante, coniugalis convictus restaurandus est, nisi ab auctoritate ecclesiastica aliter statuatur.

§ 1. A spouse who occasions grave danger of soul or body to the other or to the children, or otherwise makes the common life unduly difficult, provides the other spouse with a lawful reason to leave, either by a decree of the local Ordinary or, if there is danger in delay, even on his or her own authority.
§ 2. In all cases, when the reason for separation ceases, the common conjugal life is to be restored, unless otherwise provided by ecclesiastical authority.

SOURCES:
§ 1: c. 1131 § 1; CI Resp. III, 25 iun. 1932 (AAS 24 [1932] 284)
§ 2: c. 1131 § 2

CROSS-REFERENCES: c. 1152

1. Grave spiritual danger (c. 1153 § 1)
     Canonical doctrine has tended to interpret this cause for separation as protection of the religious life of a person when either his or her salvation or the peaceful practice of his or her faith could be in danger. In short, it has come to be identified with inducement to sin. This interpretation was supported in c. 1131 of the CIC 17 by the words grave seu animae, which were interpreted in a theological sense. Although the expressions grave seu animae (c. 1131 of the CIC 17) and grave seu animi (c. 1153 § 1) can be understood in various senses, this cause for separation has come to be identified with protection of the Catholic faith of the spouse and children. This may be because other values are safeguarded by the causes for separation that protect the temporal good of the person or peaceful cohabitation, as indicated by Bernárdez. (2)
     There is grave spiritual danger when a spouse expressly or tacitly, positively and repeatedly incites his or her spouse or children to commit grave sins, or prevents them from meeting their religious obligations.

2. Grave bodily danger (c. 1153 § 1)
     There is bodily danger when, for any reason, there is danger to the personal safety or health of the spouses or children as a result of cohabitation. Through this cause for separation, the legislator protects the lawful right every person has to do what is necessary to preserve his or her own life and personal safety, as that of his or her children, especially if they are minors and cannot act on their own behalf.
     These threats or dangers may come from the malice of the other spouse, as well as from causes for which neither spouse is directly responsible. It will result from a spouse’s malice when, for example, he or she attacks the other spouse or their children, threatens them with death or grave bodily harm, or when it is seriously and justifiably foreseen that this can occur at any time, without prior threats. It will proceed from causes without fault on the part of either spouse when one from a serious contagious illness or a state of insanity and there is no other way of avoiding the danger.
     Consequently, if one spouse places the other or the children in grave bodily danger, he or she is providing a lawful reason to separate, whether or not the danger can be morally imputed to him or her.
     Grave bodily danger is a concept where the irrelevance of the spouse’s fault can acquire greater importance. Certainly the danger is enough without fault for there to not be a duty to live together. Moreover, not living together can even be a duty, as with serious contagious illnesses, aggressive insanity, etc. In these latter cases, the judge must investigate the seriousness of the illness or the danger of the mentally ill person to proceed with maximum justice, defending the personal safety of the spouse and children but also protecting the principle of mutual assistance that governs. For lawful separation, the situation that is contrary to conjugal life must be a fault or irremediable through other means.

3. Grave danger in common conjugal life (c. 1153 § 1)
     According to c. 1153 § 1, there is a legitimate cause for separation when a spouse makes common life too difficult. Making the common life unduly difficult is a generic expression that indicates a series of varied circumstances, which can make conjugal cohabitation very difficult or impossible. With this expression, the legislator makes way for all those manifestations of cruelty, verbal or physical abuse, harshness, and lack of consideration towards another, that produce a common life that is practically impossible.
     Physical cruelty includes violent conduct and physical aggression against one’s spouse or one’s material assets, cruel or merciless treatment, through beating, etc. Moral cruelty involves offensive conduct, in word, act, or omission, against the dignity, honor, and feelings of the person, through slander, insults, disregard, etc.  For separation due to physical or moral cruelty to be lawful, the following is necessary:
— it must be grave, such that it makes common life dangerous for the spouse or children;
— it must be repeated, because if it were merely occasional, it would not create the fear for future common life, which justifies the separation;
— and separation must constitute the only means of avoiding the danger involved in common life.

4. Malicious abandonment
    The concept of malicious abandonment as a sufficient cause for separation is not expressly provided by current legislation. Its autonomous treatment and character regarding the other concepts of separation is the result of a work of jurisprudence and doctrine with the intent of specifically protecting compliance with every conjugal and family duty, penalizing their omission (3).
     It is differentiated from other causes of separation in that, while causes expressly defined in the CIC contemplate positive conduct —”occasions grave danger of soul or body to the other or to the children, or otherwise makes the common life unduly difficult”—, malicious abandonment contemplates noncompliance with every conjugal duty.
     Malicious abandonment is a negative situation or negative conduct of noncompliance with every conjugal duty. The party abandoning one’s spouse violates one’s matrimonial duties, that is, he or she fails to comply with the principle foedus nuptiale servandum est, because the spouse’s attitude consists precisely of a dissolution, in the sphere of social reality, of the conjugal consortium.
     Malicious abandonment constitutes a cause for temporary separation, based on a principle distinct from those that are the basis in other causes of temporary separation: violation of the principle foedus nuptiale servandum est. While the criterion for admissibility of a factual situation as a cause of separation is none other that that of implying a clear and unequivocal violation of one of the five principles informing married life (see commentary to c. 1151, 2), and cc. 1152 and 1153 are deduced from an analysis thereof, malicious abandonment is defined as the break-up of the conjugal consortium on the plane of social reality.
    With the concept of malicious abandonment, one is not seeking separation, because in fact it already exists; nor avoiding danger to the spirit or body of the other spouse, which can be involved in cohabitation, in that there is no longer cohabitation. With invocation of the concept of malicious abandonment, there is an attempt to declare guilty the spouse who has maliciously been absent and to obtain the legal declaration of separation for the one who has been abandoned.
     Because of its importance as a cause for separation, which requires fault on the part of the absent spouse, jurisprudence indicates the following requirements for malicious abandonment:
a) Abandonment or separation of fact. There must be de facto abandonment or separation. Abandonment is understood to exist if the spouse leaves the conjugal domicile or prevents the other spouse from entering it.
b) Intent to disavow the fulfillment of conjugal duties. The departure from the conjugal domicile must take place with the desire to abandon compliance with conjugal rights or obligations. A temporary absence to fulfill a lawful and reasonable objective does not constitute malicious abandonment.
c) Without just cause. There must not be any just cause for the unilateral decision to depart from the conjugal domicile.
In short, the concept of malicious abandonment is the procedure to convert a de facto separation unjustly created by one of the spouses into a de jure separation.

5. Form of establishing temporary separation (c. 1153 § 1)
     Conjugal separation is a matter of interest to the public good and cannot be done without the intervention of the public authority. In a marriage between baptized persons, this intervention belongs to the competent ecclesiastical authority. Nevertheless, c. 1692 § 2 indicates that “Where the ecclesiastical decision does not produce civil effects, or if it is foreseen that there will be a civil judgement not contrary to the divine Law, the Bishop of the diocese in which the spouses are living can, in the light of their particular circumstances, give them permission to approach the civil courts” (vide commentary to c. 1692).
     Since the intervention of the public authority is necessary for temporary separation, this separation can take place, as an exception, on the spouses’ own authority, if there is a legitimate cause for separation and a delay involves danger.

(1)  On the causes of conjugal separation, see A. Bernárdez Cantón, Las causas canónicas de separación conyugal, Madrid 1961.
(2)  Cf. A. Bernárdez Cantón, Compendio de Derecho Matrimonial Canónico, 7th ed., Madrid 1991, p. 269.
(3)  Cf. J. Hervada, “Observaciones sobre el abandono malicioso y la restauración de la vida conyugal,” in Idem, Vetera et Nova, Pamplona 1991, pp. 69?119; A. Fernández Coronado, El abandono malicioso. Estudio jurisprudencial, Madrid 1985; A. Bernárdez Cantón, “El abandono malicioso como causa de separación conyugal,” in Revista Jurídica de Cataluña 59 (1960), pp. 167?203.