That must have been one confusing mess.
That's something else that bugs me about this. I don't know this person. I may think he's an upstanding individual otherwise, and I may appreciate what he's done for her on some level, but I just don't really want anything to do with him.
Perhaps I should elaborate. She was in a very bad way before she left, feeling closed off and disconnected from everyone else. She felt she had to be a rock, an inhuman, "perfect" thing. As I understand it, this person was capable of breaking down her walls and drawing her out, making her comfortable with herself. I'm kind of frustrated that I had my head up my ass for so long that I couldn't even fix her, let alone myself.
So that's why he's so special to her. Watching them converse long-distance, I find myself having trouble wrapping my head around them. It seems he's into his own research and has attractions for others; as much as she may mean to him, I don't think he's pursuing anything permanent. If anything, he may see it as a special FWB thing.
Regarding her, I have no idea how she'd react if he went monogamous with someone else. I get the idea she's more interested in him than the other way around. He was there when she was most vulnerable. He was capable of "saving" her in her mind. It's definitely a strong source of attachment.