Whew! Your responses have really helped me feel less crazy and like my concerns are much more reasonable. Talked with the SO a bit more about it too-- he personally says he's trying the "teach to fish" method. However, she is awfully clingy to him and he can only do so much. He also wanted me to mention something I left out of my story and that is that he has been trying, in his view, to set boundaries with her and make the nature of the new (friendship/support, not romantic) relationship clear to her and also make it clear(er) that a new romantic relationship is unlikely at best, but she doesn't want to hear it and says she needs the hope to stay stable.
I do think he's got a bit too much white knight in him and may be being manipulated, though. Consciously on her part or not.
I'm talking with her over coffee tomorrow and hopefully me laying out my view, boundaries, and the situation will help. Who freaking knows... Wish me luck and thanks all!