From the USCCB - *Marriage: Love and Life in the Divine Plan
A Pastoral Letter of the United States Conference of Catholic Bishops
In some cases, divorce may be the only solution to a morally unacceptable situation. A
specific example is a home where the safety of a spouse and children is at risk. As the Catholic bishops of the United States, we reiterate what we said in our pastoral message on domestic violence, When I Call for Help, namely, that no one in a marriage is obliged to maintain common living with an abusing spouse.38 We want to assure people who are caught in the tragedy of an abusive marriage that the Church is committed to offering them support and assistance.*
CCC - 2383 The separation of spouses while maintaining the marriage bond can be legitimate in certain cases provided for by canon law.177 (1649)
If civil divorce remains the only possible way of ensuring certain legal rights, the care of the children, or the protection of inheritance, it can be tolerated and does not constitute a moral offense.
I don’t know how much more practical it can get. If one wants an answer to a specific marital situation then that person should speak to their priest.
The Church accepts that some circumstances will demand separation and in some cases a legal divorce. No one is obligated to submit themselves or children to serious danger, be that physical or psychological.
Separation is permissible when there is adultery - even if the adulterer is repentant. The Church strongly encourages forgiveness and reconcilliation, but it is not required. The decision remains the right of the innocent spouse (as below):
Can. 1152 §1. Although it is earnestly recommended that a spouse, moved by Christian charity and concerned for the good of the family, not refuse forgiveness to an adulterous partner and not disrupt conjugal life, nevertheless, if the spouse did not condone the fault of the other expressly or tacitly, the spouse has the right to sever conjugal living unless the spouse consented to the adultery, gave cause for it, or also committed adultery.
§2. Tacit condonation exists if the innocent spouse has had marital relations voluntarily with the other spouse after having become certain of the adultery. It is presumed, moreover, if the spouse observed conjugal living for six months and did not make recourse to the ecclesiastical or civil authority.
§3. If the innocent spouse has severed conjugal living voluntarily, the spouse is to introduce a cause for separation within six months to the competent ecclesiastical authority which, after having investigated all the circumstances, is to consider carefully whether the innocent spouse can be moved to forgive the fault and not to prolong the separation permanently.