This commentary is based on my notes after reading The New International Commentary on the Old Testament: Song of Songs, by Tremper Longman III, 2001
Poem 19 (Ch 8)
(Public Displays of Affection)
v 1 Oh, that you were like my brother,
who sucked at the breast of my mother!
Then I would find you in public and kiss you,
and they would not shame me.
The woman is wishing that it was socially acceptable for the couple to show affection (a friendly kiss) in public as one would with a brother or sister. This shows the backwardness of societal rules, where a married couple, who should rightly be affectionate, are required to be more chaste than two people who are not as intimate. It is therefore acceptable, for married couples show a modicum of affection in public.
The reason for defining that they have the same mother is that polygamy is common during this time and siblings with different mothers would not be as close as they would not be raised in as close a proximity. Brothers and sisters with the same mother would also have the same father, and as full siblings they would not be able to marry as half siblings could.
v 2 I would lead you; I would bring you
to the house of my mother who taught me.
I would make you drink spiced wine,
from my own pomegranate wine.
Since pomegranates symbolize fertility, this is likely a euphemism for sexuality. Her mother’s house is likely a home in the city, where the two can get away instead of having to go all the way home.
This section also implies that it is her mother who taught her about intimacy. In a culture without sex education, the internet and where books are expensive there is no other place to learn. It also implies that parents should teach their children the facts of life.
v 3 His left hand is under my head,
and his right hand embraces me.
They are laying together.
v 4 I adjure you, daughters of Jerusalem,
do not awaken and do not arouse love until it desires.
The woman is again warning the single women not to rush into love, but to wait until it is right. The implication is that if you do not wait, it will not be as wonderful as what she has.