Night Song by Beverly Jenkins - this is the first book by the First Lady of African American Romance, from 1994.  Cara is a schoolmarm.  Chase is a Buffalo Soldier.  They do it.  A lot.  All over the house, y'all.  All over the house.  Also there are some murders.

There is no sexual assault in the present of this book; however, several characters tell the traumatic stories of their pasts under slavery and one does include rape.  There's also a romance novel-y rape threat by the villain but it doesn't actually happen, and an equally romance novel-y miscarriage (no vivid details.)