The Lord Jesus would never have chosen a woman who didn't vow to remain a virgin

"You had good reason to be horrified at the thought that another birth might issue from the same virginal womb from which Christ was born according to the flesh.  For the Lord Jesus would never have chosen to be born of a virgin if He had ever judged that she would be so incontintent as to contaminate with the seed of human intercourse the birthplace of the Lord's body, that court of the Eternal King."

- Saint Siricius, Letter to Anysius, Bishop of Thessalonica, 390.

From Brother Anthony Opisso, a Cistercian monk:

"From the earliest biblical days adultery carried with it a sense of defilement, so that a woman who had know contact with another man, even if by force, was considered no longer fit to be visited by her husband (Genesis 49:4; 2 Samuel 20:3, re ibid. 16:21-22; Book of Jubilees 33:6-9; Epstein, Marriage Laws in the Biblical Talmud, p.51).
The deuteronomic code teaches that a woman who is divorced by her husband and thereafter marries another man likewise cannot return to her former husband (Dt 24:1-4). As the Lord said through the prophet Jeremiah: "If a man put away his wife and she goes from him and becomes another man's wife, shall he return to her again, shall not the land (his wife's body) be greatly polluted?" (Jr 3:1; see Targum to Dt 24:1-4).

In rabbinic law a woman who has committed adultery is "defiled" and cannot remain the wife of her husband, but must be divorced (Sifre on Dt, edit. M. Friedman (1864) 270 p. 122b; Sifre on Numbers, edit. M. Friedman (1915) 7 p. 4a and 19 p. 66). Furthermore any intimate male contact by the wife with Jew or gentile, potent or impotent, natural or unnatural makes divorce compulsory (Sotha 26b; Yebamoth 55a, b, 87b; Kethuboth 9a, Babylonian Talmud; Kethuboth 25a; Sotah 27a, Yad, Sotah 2,2, Jerusalem Talmud).
Betrothed

In Jewish Law a man betrothed to a woman was considered legally married to her. The word for betrothed in Hebrew is Kiddush, a word that is derived from the Hebrew word Kadash which means "holy" "consecrated," "set apart." Because by betrothal (as in Mt 1:18; Lk 1:27) , or marriage, a woman became the peculiar property of her husband, forbidden to others.

The Oral Law of Kiddushin (Marriages and Engagements) states; "The husband prohibits his wife to the whole world like an object which is dedicated to the Sanctuary" (Kiddushin 2b, Babylonian Talmud).

We know from the Gospel of Matthew 1:14 that Joseph the husband of Mary was a righteous man, a devout law-abiding Jew. Having noticed that Mary was pregnant and that he, her betrothed, had nothing to do with the pregnancy, Joseph had either to publicly condemn her and have her put to death for adultery (Dt 22:22-29) or put her away privately.

His decision was made when an angel appeared to him in a dream, saying: "Joseph, son of David, do not fear to take Mary as your wife; for that which is conceived in her is of the Holy Spirit; she will bear a son, and you shall call His name Jesus, for He will save His people from their sins" (Mt. 1:20-21). The angel does not use the phrase for marital union: "go in unto" (as in Gn 30:3, 4, 16) or "come together" (Mt 1:18) but merely a word meaning leading her into the house as a wife (paralambano gunaika) but not cohabiting with her.
For when the angel revealed to him that Mary was truly the spouse of the Holy Spirit, Joseph could take Mary, his betrothed, into his house as a wife, but he could never have intercourse with her because according to the Law she was forbidden to him for all time.
Marriage to the Holy Spirit

We also have to take into consideration that when Mary was told by the archangel Gabriel "Behold, you shall conceive in your womb, and bring forth a Son, and you shall call His name Jesus" (Lk 1:31), he also added that this was to come about because "The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the Holy one to be born shall be called the Son of God" (Lk 1:35).

By stating it in those terms the archangel declared to Mary that God would enter into a marital relationship with her, causing her to conceive His Son in her womb, For "to lay one's power (reshuth) over a woman" (Targum to Dt 21:4) was a euphemism for "to have a marital relationship with her."

Likewise "to overshadow" (Lk 1:35) by spreading the "wing" or "cloak" over a woman was another euphemism for marital relations. Thus, the rabbis commented (Midrash Genesis Rabbah 39.7; Midrash Ruth Rabbah 3.9) that Ruth was chaste in her wording when she asked Boaz to have marital relations with her by saying to him "I am Ruth you handmaid, spread therefore your cloak ( literally, "wing": kanaph) over your handmaid for you are my next-of-kin" (Ruth 3:9).

Tallith, another Aramaic-Hebrew word for cloak, is derived from tellal = shadow. Thus, "to spread one's cloak (tallith) over a woman" means to cohabit with her (Kiddushin 18b, see also Mekhilta on Exodus 21:8). Did not the Lord say to His bride Israel: "I am married to you" (Jr 3:14) and "your Maker is your husband"? (Is 54-5:5; Jr 31:32)? And what is more intimate than what the Lord said to His bride: "You developed, you grew, you came to full womanhood; your breasts became firm and your hair grew... you were naked... and I saw that you were now old enough for love so I spread my cloak over you... I gave you My oath, I entered into a covenant with you and you became Mine, says the Lord God" (Ezk 16:7, 8).

Mary prohibited to Joseph

Having been enlightened by an angel in a dream regarding her pregnancy, and perhaps further by Mary concerning the words of the archangel Gabriel to her at the Annunciation, Joseph knew that God had conducted himself as a husband in regard to Mary. She was now prohibited to him for all time, and for the sake of the Child and Mary he could only live with her in an absolutely chaste relationship.

Living a celibate life within marriage was not unknown in Jewish tradition. It was told that Moses, who was married, remained continent the rest of his life after the command to abstain from sexual intercourse (Ex 19:15) given in preparation the seventy elders abstained thereafter from their wives after their call, and so did Eldad and Medad when the spirit of prophecy came upon them; indeed it was said that the prophets became celibate after the Word of the Lord communicated with them (Midrash Exodus Rabbah 19; 46.3; Sifre to Numbers 99 sect. 11; Sifre Zutta 81-82, 203-204; Aboth Rabbi Nathan 9, 39; Tanchuman 111, 46; Tanchumah Zaw 13; 3 Petirot Moshe 72; Shabbath 87a; Pesachim 87b, Babylonian Talmud).

Celibacy according to tradition
Elijah and Elisha were celibate al their lives (Zohar Hadash 2:1; Midrash Mishlei 30, 105, Pirke Rabbi Eliezer 33). When for the sake of the Torah (i.e., intense study in it), a rabbi would abstain from relations with his wife, it was deemed permissible, for he was then cohabiting with the Shekinah (the "Divine Presence") in the Torah (Zohar re Gn 1:27; 13:3 and Psalm 85:14 in the Discourse of Rabbi Phineas to Rabbis Jose, Judah, and Hiya).

It is well known that the rabbis spoke concerning the obligation of all males to be married and procreated: "He who abstains from procreation is regarded as though he had shed blood" (Rabbi Eliezer in Yebamoth 63b, Babylonian Talmud; see also Shulkhan Aruch (Code of Jewish Law) section Evenhar-Ezer 1:1,3,4). According to Yebamoth 62b, B.T. a man is only half a man without a wife, citing Genesis 5:2 where it is said: "Male and female He (God) created them and blessed them, and called their name Adam (lit. "Man").

Nevertheless, "if a person cleaves to the study of the Torah (i.e., dedicates all his time to it) like Simeon ben Azzai, his refusal to marry can be condoned" (Skulkhan Arukh EH 1:4). Rabbinic scholar Simeon ben Azzai (early second century A.D.) was extraordinary in his learning: "with the passing of Ben Azzai diligent scholars passed from the earth" (Sotah 9:15). He never married and was celibate all his life so as not to be distracted from his studies, and because he considered the Torah his wife, for who he always yearned with all his soul (Yebamoth 63b). He was an outstanding scholar (Kiddushin 20a, B.T.) and also renowned for his saintliness (Berakoth 57b, B.T.).

Other celibates

Jewish tradition also mentions the celibate Zenu'im (lit. "chaste ones") to whom the secret of the Name of God was entrusted, for they were able to preserve the Holy Name in "perfect purity" (Kiddushin 71a; Midash Ecclesiastes Rabbah 3:11; Yer. yoma 39a, 40a).

Those in hope of a divine revelation consequently refrained from sexual intercourse and were strict in matters of purity (Enoch 83:2; Revelation 14:2-5).
Philo (Apol. pro Judaeis 1X, 14-17), Josephus, (Antiq. XVIII. 21) and Hipploytus (Philosophumena IX, IV, 28a) wrote on the celibacy of the Jewish Essenes hundreds of years before the discovery of their settlements in Qumran by the Dead Sea.
Philo Judaeus (c. 20 B.C.-50 A.D.), a Jewish philosopher, described Jewish women who were virgins who have kept their chastity not under compulsion, like some Greek priestesses, but of their own free will in their ardent yearning for Wisdom. "Eager to have Wisdom for their life-mate, they have spurned the pleasures of the body and desire no mortal offspring but those immortal children which only the soul that is dear to God can bring forth to birth" (Philo, Cont. 68; see also Philo, Abr. 100).
For "the chaste are rewarded by receiving illumination from the concealed heavenly light" (Zohar 11. 229b-230a). Because "if the understanding is safe and unimpaired, free from the oppression of the iniquities or passions... it will gaze clearly on all that is worthy of contemplation" (Philo, Sob. 1.5). Conversely, "the understanding of the pleasure-loving man is blind and unable to see those things that are worth seeing... the sight of which is wonderful to behold and desirable" (Philo, Q. Gen.IV.245).

Joseph as celibate caretaker

As the recipient of the great revelation that what was conceived in the womb of Mary, his betrothed, was of the Holy Spirit and that the Child to be born was destined to save His people from their sins, surely Joseph knew that he was called to take care of Mary and her Child, the Messiah, for the rest of his life, which is why the angel told him to take Mary as his wife.

We may reasonable assume that Mary herself now shared with him all that the archangel Gabriel said to her. No less a Person than "the Son of God" (Lk 1:35) was to be entrusted to his care under the shelter of his humble home, now become the Holy of Holies.

Jewish tradition mentions that, although the people had to abstain from sexual relations with their wives for only three days prior to the revelation at Mount Sinai (Ex 19:15), Moses chose to remain continent the rest of his life with the full approval of God. The rabbis explained that this was so because Moses knew that he was appointed to personally commune with God, not only at Mount Sinai but in general throughout the forty years of sojourning in the wilderness. For this reason Moses kept himself "apart from woman," remaining in the sanctity of separation to be at the beck and call of God at all times; they cited God's command to Moses in Deuteronomy 5:28 (Midrash Exodus Rabbah 19:3 and 46.3).

Again, we may be sure that Saint Joseph remained celibate all his life because throughout his married years he was in daily attendance and communication with Jesus, the incarnate Word of God."

And yet, this from Francis.