Jesus left that place and went away to the district of Tyre and Sidon. Just then a Canaanite woman from that region came out and started shouting, "Have mercy on me, Lord, Son of David; my daughter is tormented by a demon." But he did not answer her at all. And his disciples came and urged him, saying, "Send her away, for she keeps shouting after us." He answered, "I was sent only to the lost sheep of the house of Israel." But she came and knelt before him, saying, "Lord, help me." He answered, "It is not fair to take the children's food and throw it to the dogs." She said, "Yes, Lord, yet even the dogs eat the crumbs that fall from their masters' table." Then Jesus answered her, "Woman, great is your faith! Let it be done for you as you wish." And her daughter was healed instantly.

So it seems that in this fable Jesus was willing to give what is holy to a "dog".

That said, there are impediments that can render an alleged marriage invalid. Divorce must not be on the table, therefore it is invalid for a couple to enter into marriage with a prenuptual agreement in effect. Fidelity must be intended, so while subsequent adultery cannot invalidate a marriage, one cannot validly enter into marriage intending to commit adultery. The marriage must be possible to consummate, so men cannot enter into marriage with ED that cannot be treated with medication so as to enable the marital act, nor can someone whose genitals have been mutilated (whether by self, by another's malice or by disease or accidental injury) to the point where the marital act is rendered impossible. Fertility must be accepted, so it is invalid to enter into marriage refusing to be a parent. Polygamy is liturgically impossible, so someone who has been validly and sacramentally married cannot enter into another marriage while the first spouse still lives. Marriage must be entered into by the willing and competent, so fraud, duress, abduction, insanity, ignorance (of what marriage is) and being below the minimum age invalidate a marriage. Incest is forbidden, so a marriage between those of a forbidden degree of consanguinity is invalid.

I must make abundantly clear, to invalidate a marriage an impediment must have existed at the time the putative marriage was contracted, even if it not discovered until later. No subsequent action after the marriage can alter its validity. If an impediment is discovered later and has since been resolved, then the couple are free to marry each other validly. If an impediment is discovered later and the couple will not or cannot resolve it, they shall be free to marry another, but they must confess any guilt they may have incurred from attempting to contract or remain in an invalid marriage (this varies depending on the knowledge and understanding of the impediment in question).

As for nunnery itself, are you unaware that the Scriptures encourage the unmarried to swear off marriage and the widowed to swear off remarriage? Celibacy is a higher calling than marriage, and to those who can handle it, it is a great blessing. Among those capable of marriage (that is, physically capable of performing the marital act, mentally capable of understanding and freely entering into marriage and having reached the age of maturity), no one is forbidden to marry unless he or she has placed that obligation on him/herself. However, if you make a vow to the Lord, you must keep it. Therefore, those who pledge their virginity to the Lord must remain virgins until death or the Second Coming.

' Do not give what is holy to dogs or throw your pearls before pigs; otherwise they will trample them under their feet and turn around and tear you to pieces. "
~ Matthew 7:6

If one cannot "judge" i.e. discern how is one to determine who is a "dog" or a "pig" i.e. unbeliever? Besides you quoting this to me is a form of "judging" is it not? So you tell me to nor to judge while you judge and all of that with Scriptural abuse violating the context…