Is she who I think she is?

Chapter 3 brought about confusion to me. Jake was just sitting by himself at a restaurant and it says in the first paragraph of page 22 how he caught the eye of a girl and just simply by that she came down and sat with him as if they had known each other and this meeting was planned. However, after a while, I get the feeling that she may be a prostitute. Also, when she asks if Jake is sick and then she tells him that she herself is sick, I wasn't sure if they were talking about a simple cold or maybe a STD. I may be way off but this is just what came into my mind when I read through this chapter. I am also confused why Jake calls her his fiancee when he introduces her to his friends. My guess is that fiancee is not used the same way I am familiar with. For this book, I am going to read it without sparknotes so there are probably going to be many times where I am confused.