What concerns me is that funky_princess acts as if she can’t say no, if the guy wants to fuck her. She sounds as if she believes she is powerless to stop it from happening, if that’s what he wants. The very fact that she asks this questions suggests she has little sense of power for herself. She may take into account what a bunch of strangers on the internet say! Pretty scary.
The issue here is probably self-esteem. I suspect she wants to learn how to be stronger, and how to establish what she wants and then make it happen. If that’s the case, then she should tell Don Juan not to bother showing up. Just beg off with any excuse whatsoever.
I don’t think she’s a slut at all. Even if she does want a nsa roll in the hay. I think the guy knows someone who he can easily take advantage of (which is different from saying she’s easy), and feels no compunctions about picking the low-hanging (forbidden) fruit. He’s the one with dubious morals.
If I’m right, call it off. If you want a night of fun, go for it. If you want a relationship with this guy, you may want to think again. Certainly, you should get to know him better before you consider being that intimate with him.