Just wanted to give a push to a publishing site that I have come across. Circlet Press is a publisher that has well written dark erotica at its heart.
For example, The Prince’s Boy by Cecilia Tan, is a tale of a prince and his whipping boy ensnared in a plot of dark erotic magic. It explores themes of dubious consent and situations of sexual jeopardy.
Other themes cross the spectrum of LGBT.
http://www.circlet.com/