My boyfriend's ex

Alexandra
So my boyfriend's ex just appeared on his doorstep the other day. She's from an abusive home and when she was with my boyfriend she really leant on him and depended on him. From what he's told me my boyfriend ended things with her because this out too much strain on their relationship. When he left she was in a good situation and away from her family. But she kept expecting my boyfriend to turn into her dad and he couldn't take it anymore. 
Well apparently she tried to fix things at home and it got very messy. So now she here looking for support from my boyfriend. He's letting her stay at his place for the moment and has told me that he'll stay with me at my apartment if I'm more comfortable with that. He's told her he needs to talk to me about this and I know he wants to help her through this. And part of me wants him too. He's such a good person and he does care about her as a friend. And if it were me in her position I know that I'd need/want him. 
But my boyfriend has told me that he is still physically attracted to her. This happened months ago when we'd first rated seeing eachother and werent official. So there is this part of me that feels very threatened by her. In my mind she's always been that evil ex who tries to ruin your relationship. I can't get that out f my head. Part of me just wants him to kick her out and have her out of his life for good. But the compassionate voice in my head is saying that doing so would be damaging for her potentially. What would you ladies do? Any advice please?