roomate can't understand why i'm upset that she is moving out

Hi all!

Some backstory, I am a 2nd year college student who currently shares a room with a girl and a suite with two other girls as well. Me and the girl in my room have become great friends in school, even considering each other our best friends. We mostly just stick together when we hang out aside form a few separate friends. We both have a mutual dislike for the other two in our suite and have really gotten closer after the horrors we experienced with them. Our ways of living are pretty similar, so we've for the most part gotten along great for the 2 years we have lived together. Obviously we've had our disagreements, but that is typical when sharing a room with someone every single day.

Applications for next years housing at our college are about to open this week. For reference, my family, while they can afford to help send me here, did not have a savings account for my college. Hers did, so she has a lot more money than I do in terms of housing. Essentially, the only housing I can afford is on-campus housing. Sh can afford to live off-campus, but after running the numbers with my family, we've decided that we just can't make the 1500+ a month needed to afford off campus. Either way, the housing we could get together on campus would allocate each our own personal room, which is a non-negotiable for both of us.

For her, on-campus versus off campus housing costs the same either way. However for me, I get a big discount with my financial aid, making it the only affordable option. I have made it clear that I understand if she does not want to live on campus since the off campus places tend to be nicer. But that she needs to tell me ASAP.

We have discussed this several times throughout this school year. I have told her that if she would rather live off-campus, that is fine but she needs to tell me as soon as possible so I can begin making other arrangements. She assured me that she does not mind living in the on-campus since we will still be getting my own room, that we are great friends and she will stick with me no matter what. I asked her numerous times, at least 5-6, and each time, she assures me that she has no issue accommodating my finances and living in a place that my family and I can afford. For reference, I just asked her a week ago to verify that we would be living together on-campus and again, she said yes.

Well, today I come home and she says we need to talk. She told me that she has been thinking about this for months and has decided she does not want to live on campus because she would be living in "a shithole" for the same cost that she could be living in a better apartment. I calmly said "okay." What else can I say?

I fully understand the situation, however I am hurt because I have explained to her that I needed to know this months in advance and she waited to tell me this the very week we were expected to apply for housing. Now that she is leaving our roomate group, my selection date will be a week later, making my chances for getting the oncampus housing that I need very limited. I likely won't get it anymore and she knew this. Also, I could have had time to search for other roommates, but now have only a week. If I don't get this housing, I will have no option but to transfer schools and live home and commute to school in my home town.

We have both had a very stressful semester. She had a pretty bad breakup (that she primarily caused). Her ex boyfriend notified me after the breakup that she had been talking badly on me and that she thought I was a bad friend. I tried not to take this to heart but did eventually bring it up to her. She denied the claims but I can't get it out of my head. her ex is the best friend of my boyfriend by the way, so I had no foul intentions by speaking with him. It is kinda unavoidable. I did cut contact with him eventually but I keep thinking, why would he lie about that? He is a trustworthy guy. This is not the only instance I have caught her talking badly on me, but I overlook it and give her the benefit of the doubt that maybe I was annoying her, as she does me sometimes.

Since I found out, I left our place, had time to process and discuss with my family, and soak it all in. My family says that if I do not have this housing, I will have no choice other than to transfer home. So it is very possible that her lack of consideration and poor planning could cost me my chance to go to school here. I am the first in my family to go to college and it is so important and she knows this. Like I said, we are best friends.

If we did not have the relationship we had, I could understand the lack of planning, but we have been so close that this feels like a massive, unforgivable betrayal. I have not been rude to her but have been colder since the news broke. I am trying not to, but it is difficult when you find out she is bad talking you behind your back, while screwing your whole life over knowingly and simultaneously. She asked me if we were good, to which I replied, "we are fine, however i really wish you would have let me know this when you started having thoughts, not the week of room selection." She got defensive and said it is not her job to look out for my finances. She's right, but like I've said, she made a promise to me that she would accommodate, and pulled the rug from under me last minute. She said I have no right to be mad and that this is just how it goes. It has been very awkward since.

I have realized from this experience that this is not a friend who I want in my life. Someone who makes empty promises and talks badly about me to others. I told her that I don't hate her, but she screwed me over and this definitely changes the dynamic of our friendship. It's like her entire personality changes about a week ago, then she dropped this.

AITA for being upset about this? Remember this is not a peaceful coexistence situation, but a deep friendship with someone I thought would be in my life forever. Please be kind in the comments. I lost my only good friend hours from home and might be forced to leave my dream school due to her inconsideration.

TLDR - Best friend roomate has more money for housing than me. She agreed that she would be willing to accommodate my budget on housing, multiple times throughout the course of the year. A week before housing selection, she tells me she changed her mind, putting my ability to get affordable housing at risk. She has had a whole year to tell me this. If I don't get it, which is unlikely now, I will have no other option than to transfer and live at home with parents while I finish in my hometown. This all could have been avoided if she had just told me in advance her new living arrangements. She cannot fathom why I am upset about this and told me I have no right to be upset. AITA?

Edit: If I do happen to get on-campus housing (which is very unlikely now), it will very likely be a room that I have to share with another person. Which would not be so bad if I had time to roomate hunt, but could be a horror story. I do not want to be a 21 year old woman still sleeping feet away from someone else, especially a stranger.