The Torah never mentions breasts as an object of erotic fascination; they are solely nourishment for infants. In the wisdom literature, things are different. Solomon encourages young men to delight in the breasts of their wives - not of another, a strange woman (Proverbs 5) -, and in the Song Solomon speaks rapturously of the breasts of his beloved.
The progression is intriguing. Israel, it seems, is growing from infancy to hormonal young manhood. Wisdom comes into play at the same time Israel begins to notice the beauty of female bodies. Song of Songs 7:7-9 points at another aspect of this progression. Infants seek milk at the breast, but the lover thinks of his beloved’s breasts as fruit - dates at the top of a date palm, clusters of grapes on the vine. Torah is mother’s milk for Israel in infancy; wisdom is intoxicating, a lover’s wine.