It's no horror movie. What is the relationship between the 2 girls? "Friend" can have many different meanings and is a term used very loosely in Thailand (the English version of it). My girlfriend calls her new colleague at a new job a "friend" after just a week, simply because they work at the same place and sometimes have lunch together.
A lot of these "friends" will backstab each other to get to a foreigner. It's dog-eat-dog, or more aptly, friend-eat-friend, when it comes to nabbing a foreigner. It could have gone the other way just as easily.
I don't know the age difference and didn't read the original story (OP - next time, post a link to your original story), but if there is no money forthcoming in this relationship, it'll end soon enough. Perhaps the first girl is relieved to be done with the OP?