I can see how this would all feel to her as you say, however, I have reason to believe that this devolving with them was happening long before I came around. Thought I didn't know it before, I'm definitely seeing proof of it now.
Derrall - I agree that if he's wanting to continue this relationship with her that he should make more time for her. However, even after all my encouraging him to do that, he simply just doesn't. I can't make him, either he wants to or he doesn't and honestly it feels like that's an issue they need to work out. I don't know if there is anything I can or should do about this. But in the meantime I can't be trampled on in the process.
As I've said in previous responses, he didn't cut off sleeping with her when I moved in. They were already sleeping part of the time in separate areas. A couple months after I moved in though even that waned despite my encouraging him to stay with her.
sevechten - I've asked myself and him that very question... he says he doesn't know or evades the question. He avoids her advances well enough and has told me that he feels really annoyed when she tries touching him. I have tried insisting what you suggested at the risk of sticking my nose into their business. I've brought it up twice, the first time he just said he didn't know if he could do that. The other time (several months later) he twisted it around to make it sound like I was telling him he had to get rid of her.... I can only think this latter response was more about him lashing out and projecting his thoughts and feelings about himself onto me. Because I certainly never told him to get rid of her. I'd never think of such a thing... I may if she were seriously abusive, but that just isn't the case here.