A best friend after 'that person'

I met her today. She seemed to be fine and we talked as usual. We went to our lectures as always and the girl who had passed from NITC last year was with also us.

FLASHBACK!

The girl from NITC: One day after a lecture she just got really friendly with me, though she never spoke to me before this, in fact, she and her black friend used to talk things about me and my best friend, Sarah. (so Sarah hated her) She went with me for lunch, too. She was really nice to me that day and took me to her place, gave me a gingerbread biscuit. Then, the next day she met Sarah and became friends with her, too. Sarah started liking her after that. From then on, she started humiliating me at every point she could. She comes from a rich background! So spends money on everything she likes. Will go for a Starbucks, every time she needs coffee, will go to the most expensive place fr whatever she wants. And when I go for a free cup of coffee in the university's lounge, won't let go the chance of embarrassing me and making me realize that a cheapskate I am! And then, wants my best friend to be her best friend, the worst nightmare of every student!! She tried a lot of things to be close to Sarah and she, to sme extent, is close to her.

After the project weeks! (holidays)

I talked to Sarah as usual. During the project weeks the girl from NITC did all the projects with Sarah. Maybe, I fear losing her, as she is the one I talk to most of my stuff about. Who will I talk to if she isn't there? I felt bad that she, perhaps, is closer to Sarah than I am. I just don't know why would anyone come and try to part away to friends.. 

Why?!?!!!! >:(