It is difficult to be placed in that situation. I was in one when I was in college. It was very difficult because I did care to help her as a person.

What I had to do was allow myself to be present with her in safe public places, while remaining very honest. In fact, I actually was in therapy at the time and used that relationship as a way to practice being the type of person my T was for me.
So I would be clear about things and then ask her to tell me what my words brought up for her. Honestly most of the time I just made her mad at me, but her obsession kept her from runnung out the door. So she would stay and tell me what she felt. And that was EXACTLY what I was trying to get her to do.

She eventually figured out that I was not going to "dump" her as a human the way many others had done just because she was highly expressive. But I was also not going to change my boundary lines.

Eventually she found another woman to stalk and left me alone. She tried to make me think she was dumping me and all that stuff. I had to remind her that my feelings towards her were always the same... that I cared for her as a friend and fellow human... and that I would be there is she ever needed to talk.

About two years later I saw her around. She rushed up to me and asked for a hug. We had a ver appropriate one. And she thanked me for being there for her during that time. She told me how she knew she had a problem but noone had stuck with her in the right way long enough for her to find her own way. Now she had.

Just wanted to share that with you. It is important that you first take care of yourself. After that, do what you feel is right to do.