Wow, this is dark but I really loved reading it. I love how she's broken enough that she believes that she loves them and they love her. She doesn't talk back, she's more concerned about Rodolphus' health than what Bellatrix is doing to her.
I like the bit of humanity from Bellatrix at the end, where she's agreed that it's enough and asks her husband to heal Hermione, as though she actually cares that Hermione is hurt.
Great story :)