Classical astrology writes about sex in the register in which it writes about property and health, which is to say practically and without embarrassment, and it writes about it mostly under other headings. Marriage has a chapter. The quality of the soul has a chapter that covers appetite and excess. The electional books cover the timing of a union. There is no chapter called sex, and the material has to be assembled.
The assembly produces two distinct threads, and they should not be run together. One concerns union with a named other person, and it lives in the seventh house, in Venus, and in the aspects between the lights. The other concerns desire as a disposition of the native, and it lives in Mars, in the condition of the Moon, and in Ptolemy's treatment of the irrational part of the soul. A chart can say a good deal about the second and much less about the first than practitioners have often claimed.
Modern astrology adds Pluto, discovered in 1930 and given rulership of Scorpio in the twentieth century scheme, and reads it for compulsion, taboo and transformation. Traditional practice rejects the outer planet rulerships outright and keeps Mars as Scorpio's only lord. That is a live disagreement with practitioners on both sides, and the atlas records it as one rather than settling it.
Living traditions are described here, not instructed. Nothing in this entry is guidance.