This is now the story that started my career as Black Bull for couples. My best friend and his lovely beautiful tiny little Hispanic wife are my first experience at it.
A wife and mother is brokenhearted by her husband's request for a divorce. An aging, black stranger takes advantage and greedily worms his way into her life. However, her continuing attempts to resist slowly strengthen her resolve. Will she eventually free herself from his domination? (I abhor racism in the real world, but I don't object to using a fetish trope in a sex-fantasy. The primary person of color is just a bad dude unable to cope with his troubles. His color has little to do with it.)