A novel must contain one or both of the following elements: Eros and Agon. Of the two, Eros is the hardest to write about.
In writing about sexual love, it is also necessary to try to avoid turning one of the characters into the sex object of the other. They must both have equal focalisation, or it risks becoming pornography.
The difference between writing erotica and pornography is one of crudity. Erotica is ironic or poetic, pornography is crude. In writing about sex, pornography is never far away. This is because the words for the body parts involved in the sex act, in English at least, are crude.
However, a lot depends on the audience. An ill-considered titter from the back row can destroy the noblest of intentions. And in the English psyche, sex and titter are inexorably linked.
Notes written by Murr after a close one-handed study of the entire works of the Marquis De Sade, and following his subsequent attempts to write his own pornography.