Drain Me by Lana Sky

When diagnosed with a fatal illness at the age of twenty six, Eleanor Gray is resigned to her fate—at least until the enigmatic Dublin Helos appears and makes her an offer she knows she should refuse:
Life or Death?
With a decision as harmless as checking the wrong box on a mysterious questionnaire, Ellie is plunged into a dangerous world where souls are sold to the highest bidder and pleasure is fueled by pain.
The rules of this new life are simple: submit everything—mind, body and soul. But the further Ellie falls under Dublin’s control, the more she comes to realize that it’s not just her sanity at stake, but her heart and a whole lot of blood too.