AITA for not letting my former roommate and our friend stay in my dorm?

I, 18F, recently began my spring semester of college, where I live on campus. During my fall semester, I had a roommate, Alex, 19F. Who I went to high school with, we weren’t that close in high school, but figured it might be cool to be roommates. Alex is a girl who refers to herself as a loser and in no other way (she’s actually pretty chill). She would tell people I hung out with her to be seen as someone who "takes pity on the less fortunate" when that was never the case. I just thought we could get along and have fun.

When we started the fall semester, she told her college summer camp friends that I was the Regina George of our hs, and my two best friends were the other two girls. My best friends and myself have never viewed ourselves that way nor have we ever acted that way. Our High school wasn’t the biggest, but it was big enough that I still don’t know half of the people that went there, and vice versa. So when I finally moved on campus, all of these people already had their opinions about me because of her.

We became pretty good friends until she was having issues with other people and using me as a bodyguard wherever we went somewhere without telling me anything. She had a problem with this guy who was stalking her; she used me as a way to scare him off due to my resting bitch face. It was an awkward fall semester for me.

So we all go on winter break, and a week before we go back to campus for the spring semester, she texts me that she doesn’t have the money to stay on campus anymore and still go to school. She also tells me that her mother got their 7th eviction notice, after her mother kept buying everyone, including me, expensive Christmas presents (which her mom blames me for). She then told me that she’s gonna buy a car from Facebook market with "all the money I’m saving and not wasting like you". I didn’t have a job or any money to waste.

I tell her that I’m sad about it but encourage her to do what she needs to do… She then tells me not to put the two beds together for myself, but keep "her bed" where it is so she can stay when she’s tired of her mom. She told me to file for a single room, which is $1,750 extra, and let her "sleep over when she wants, cause it used to be her room too".

After I move back into the dorm, I text our friend Kelsey, 18F, who lives in a separate building on campus and is much closer to Alex than I am, to see if she wants to get breakfast. She texts me back right away with laughing emojis… turns out she moved out because Alex moved out and didn’t want to let me know because "it was none of my business".

Now I’m alone on campus, and they talk about the fun hangouts that they purposefully don’t invite me to. They call me rude and not a good friend because I won’t let them stay in MY dorm, which I pay for, whenever they want. They stare at me in class and follow me just because they can… So AITA?