Seinen is a demographic aimed toward "Young Adult men" and Jousei is aimed toward "Young adult women"
Seinen and Jousei manga deal with mature themes compared to their younger counterparts, "Shounen" and "Shoujo". That means Seinen manga may have the same kind of content as Shonen manga but can deal with more darker elements with more realism, it can deal with sex and nudity which cannot be present in the younger counterpart, and the same goes for Jousei and Shoujo.
What you're searching for does lies in the category of Seinen and Jousei but since your focus is mostly on sex, you're better off using the "Pornographic" and "Erotica" tag in the advanced search for what you're searching for.
