So ever since i was around 14 (I am 18 now) Girls were always into me, because i am decent looking but i have a really explosive personality when talking about things i care about, this really attracts girls.

Anyway so a couple months back i ended up charming this girl, (She is sat behind me, i didnt really like her even tough she is like an 8/10 but i needed someone to talk as i was bored in class) Me being me i was oblivious to her liking me, but one day she just comes to me and asks me out, and i just reject her because i was really not interested in her.

Fast forward until today, and i have found myself somewhat attached to this girl (I know she liked me literally a couple days ago) But now she magically somehow lost interest in me in the span of literally a day because she has been talking to a friend of mine.

So the question to you guys is, Am i right for denying this girl considering how quickly she just changed who she liked? ontop of this, while she was trying to get me to like her, she literally had a fuck buddy and kept on trying to hide it becoming very frustrated whenever one of her friends mentioned anything about him around me. Would getting attached to this girl end up hurting me because of her degenerate tendencies of just magically switching to another guy.

For some background i know some very loyal women, that even tough i never really talked to them much literally liked me since middle school, and still fucking like so many years later in high school, but somehow this one girl just one days decided to jump ship.

Is this sort of behaviour a red flag?