She has a point, and while he does intend to come back some day, it's clear that he isn't going to convince her of this until it happens. "I let everyone down already. I don't want to do it again." He'll leave it at that. She can make what she wants of it.

"I'm not that type. I don't know what I would do if I stayed here." She's already determined that he won't, so admitting that doesn't seem like it will make much difference. "Which is one of the things I need to figure out. I'm not the professor type, but what am I?"