Part I: Shomer Negiah
רמב"ן:
מעשים כגון חיבוקים ונישוקים אינם מפרים מצוות לא יעשה של התורה , אלא איסור דרבנן בלבד
Ramban:
Acts such as hugging and kissing do not violate a negative commandment of the torah, but only a rabbinic prohibition.
(א) להתרחק מן העריות ובו ז סעיפים:
צריך אדם להתרחק מהנשים מאד מאד ואסור לקרוץ בידיו או ברגליו ולרמוז בעיניו לאחד מהעריות ואסור לשחוק עמה להקל ראשו כנגדה או להביט ביופיה ואפילו להריח בבשמים שעליה אסור ואסור להסתכל בנשים שעומדות על הכביסה ואסור להסתכל בבגדי צבעונים של אשה שהוא מכירה אפי' אינם עליה שמא יבא להרהר בה. פגע אשה בשוק אסור להלך אחריה אלא רץ ומסלקה לצדדין או לאחריו ולא יעבור בפתח אשה זונה אפילו ברחוק ד' אמות והמסתכל אפילו באצבע קטנה של אשה ונתכוין ליהנות ממנה כאלו נסתכל בבית התורף (פי' ערוה) שלה ואסור לשמוע קול ערוה או לראות שערה והמתכוין לאחד מאלו הדברים מכין אותו מכת מרדות ואלו הדברים אסורים גם בחייבי לאוין:
(1) A person must stay very far from women. He is forbidden to signal with his hands or his feet, or to hint with his eyes, to one of the arayos. He is forbidden to be playful with her, to be frivolous in front of her, or to look upon her beauty. Even to smell the perfume upon her is forbidden. He is forbidden to gaze at women doing laundry. He is forbidden to gaze at the colorful garments of a woman whom he recognizes, even if she is not wearing them, lest he come to have [forbidden] thoughts about her. If one encounters a woman in the marketplace, he is forbidden to walk behind her, but rather [must] run so that she is beside or behind him. One may not pass by the door of a promiscuous woman, even four cubits [around 6–8 ft] distant. If one gazes even at the little finger of a woman with the intent to have pleasure from it, it is as though he gazed at her shameful place. It is forbidden to listen to the voice of an ervah (woman who is not his wife or close relative) or to look at her hair. If one intentionally does one of these things, we give him lashes of rebellion. These things are also forbidden in the case of ordinary Biblical prohibitions.
Part II: Marriage Laws
(ו) הַמַּדִּיר אֶת אִשְׁתּוֹ מִתַּשְׁמִישׁ הַמִּטָּה, בֵּית שַׁמַּאי אוֹמְרִים, שְׁתֵּי שַׁבָּתוֹת. בֵּית הִלֵּל אוֹמְרִים, שַׁבָּת אֶחָת. הַתַּלְמִידִים יוֹצְאִין לְתַלְמוּד תּוֹרָה שֶׁלֹּא בִרְשׁוּת, שְׁלֹשִׁים יוֹם. הַפּוֹעֲלִים, שַׁבָּת אֶחָת. הָעוֹנָה הָאֲמוּרָה בַתּוֹרָה, הַטַּיָּלִין, בְּכָל יוֹם. הַפּוֹעֲלִים, שְׁתַּיִם בַּשַּׁבָּת. הַחַמָּרִים, אַחַת בַּשַּׁבָּת. הַגַּמָּלִים, אַחַת לִשְׁלֹשִׁים יוֹם. הַסַּפָּנִים, אַחַת לְשִׁשָּׁה חֳדָשִׁים, דִּבְרֵי רַבִּי אֱלִיעֶזֶר:
(6) With regard to one who vows that his wife may not derive benefit from marital relations with him, Beit Shammai say: He may maintain this situation for up to two weeks, but beyond that he must divorce her and give her the payment for her marriage contract. Beit Hillel say: He must divorce her if it continues beyond one week. Apropos the husband’s obligation to his wife regarding marital relations, the Gemara mentions other aspects of this issue: Students may leave their homes and travel in order to learn Torah without their wives’ permission for up to thirty days, and laborers may leave their homes without their wives’ permission for up to one week. The set interval defining the frequency of a husband’s conjugal obligation to his wife stated in the Torah (see Exodus 21:10), unless the couple stipulated otherwise, varies according to the man’s occupation and proximity to his home: Men of leisure, who do not work, must engage in marital relations every day, laborers must do so twice a week, donkey drivers once a week, camel drivers once every thirty days, and sailors once every six months. This is the statement of Rabbi Eliezer.
Part III: Yibbum (levirate marriage)
The story of Tamar (adapted from the Jewish Women's Archive):
Tamar is the daughter-in-law of Judah, who marries Judah’s firstborn son, Er. When Er dies, leaving no son to inherit his land, Judah gives Tamar to his second son, Onan, who is to act as levir, a surrogate for his dead brother who would help Tamar to beget a son to inherit Er’s lineage. In this way, Tamar too would be assured a place in the family.
However, Onan opts to preserve his financial advantage (as he would otherwise inherit Er's land) and intentionally sabotages his coitus with Tamar, either by pulling out or by having anal sex. For this, G-d punishes Onan with death.
Judah, however, does not know G-d’s will, and believes she has killed two of his sons. He refuses her right to beget a child with his third son, leaving her unable to financially support herself or remarry. However, she ultimately tricks Judah into impregnating her, dressed as a veiled prostitute, and therefore secures her place in the family.
(5) When brothers dwell together and one of them dies and leaves no son, the wife of the deceased shall not become that of another party, outside the family. Her husband’s brother shall unite with her: he shall take her as his wife and perform the duty of levirate marriage.